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CBSEClass10Science
SamplePaper02(2019-20)
MaximumMarks:80
TimeAllowed:3hours
GeneralInstructions:
i. Thequestionpapercomprisesthreesections–A,BandC.Attemptallthesections.
ii. Allquestionsarecompulsory.
iii. Internalchoiceisgivenineachsection.
iv. AllquestionsinSectionAareone-markquestionscomprisingMCQ,VSAtypeand
assertion-reasontypequestions.Theyaretobeansweredinonewordorinonesentence.
v. AllquestionsinSectionBarethree-mark,short-answertypequestions.Thesearetobe
answeredinabout50-60wordseach.
vi. AllquestionsinSectionCarefive-mark,long-answertypequestions.Thesearetobe
answeredinabout80–90wordseach.
vii. Thisquestionpaperconsistsofatotalof30questions.
SectionA
1. Breakingandmakingofbondsinchemicalreactioniscalledas-
2. Byconsideringtheirpositionintheperiodictable,whichoneofthefollowing
elementswouldyouexpecttohavemaximummetalliccharacteristic?
Ga,Ge,As,SeandBr
3. Answerthequestionsthatfollowsonthebasisofyourunderstandingofthe
followingparagraphandtherelatedstudiedconcepts:
Inancienttimes,woodwasthemostcommonsourceofheatenergy.Theenergyof
flowingwaterandwindwasalsousedforlimitedactivities.Theexploitationofcoalas
asourceofenergymadetheindustrialrevolutionpossible.Increasing
LAKSHYA STUDY POINT
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industrialisationhasledtoabetterqualityoflifeallovertheworld.Ithasalsocaused
theglobaldemandforenergytogrowatatremendousrate.Thegrowingdemandfor
energywaslargelymetbyfossilfuels–coalandpetroleum.Ourtechnologieswere
alsodevelopedforusingtheseenergysources.Butthesefuelswereformedover
millionsofyearsagoandthereareonlylimitedreserves.Fossilfuelsarenon-
renewablesourcesofenergy,soweneedtoconservethem.Ifweweretocontinue
consumingthesesourcesatsuchalarmingrates,wewouldsoonrunoutofenergy.In
ordertoavoidthis,alternatesourcesofenergywereexplored.
i. Whatdoyoumeanbynon-renewablesourcesofenergy?
ii. Writefiveexamplesofnon-renewableenergysources.
iii. Whichisthemainelementinfossilfuels?
iv. Whichtypeofenvironmentalhazardisnotcontributedbythecombustionoffossil
fuels?
4. Inanimals,controlandcoordinationareprovidedbynervousandmusculartissues.
Touchingahotobjectisanurgentanddangeroussituationforus.Weneedtodetect
it,andrespondtoit.Howdowedetectthatwearetouchingahotobject?All
informationfromourenvironmentisdetectedbythespecialisedtipsofsomenerve
cells.Thesereceptorsareusuallylocatedinoursenseorgans,suchastheinnerear,
thenose,thetongue,andsoon.Sogustatoryreceptorswilldetecttastewhileolfactory
receptorswilldetectsmell.Thisinformation,acquiredattheendofthedendritictip
ofanervecellsetsoffachemicalreactionthatcreatesanelectricalimpulse.This
impulsetravelsfromthedendritetothecellbody,andthenalongtheaxontoitsend.
Attheendoftheaxon,theelectricalimpulsesetsoffthereleaseofsomechemicals.
Thesechemicalscrossthegap,orsynapse,andstartasimilarelectricalimpulseina
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dendriteofthenextneuron.Thisisageneralschemeofhownervousimpulsestravel
inthebody.Asimilarsynapsefinallyallowsdeliveryofsuchimpulsesfromneurons
toothercells,suchasmusclescellsorgland.
Answerthefollowingquestions:
a. Whatistheroleofaxon?
b. Fromwhereelectricalimpulsetravels?
c. Namethechemicalwhichreleasedattheendofaxontotransmitthesignaltothe
otherneuron.
d. Thenervoussystemusesthe________totransmitmessage.
i. Electricalsignal
ii. Chemicalsignal
iii. Bothelectricalandchemicalsignal
iv. Noneoftheabove
5. Iftheangleofincidenceisincreasedforapairofair–glassinterface,thentheangle
ofrefractionwill
a. increase
b. remainsthesame
c. decrease
d. firstincreasesandthendecreases
OR
Thefocallengthoftheeyelensincreaseswheneyemuscles
a. Contractandlensbecomesthinner
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b. arerelaxedandlensbecomesthicker
c. arerelaxedandlensbecomesthinner
d. contractandlensbecomesthicker
6. Oppositiontotheconstructionoflargedamsindueto-
a. Environmentalreasons
b. Socialreasons
c. Alloftheabove.
d. Economicreasons
7. Thephenomenaofelectromagneticinductionis
a. theprocessofgeneratingmagneticfieldduetoacurrentpassingthroughacoil
b. theprocessofchargingabody
c. theprocessofrotatingcoilofanelectricmotor.
d. producinginducedcurrentinacoilbytherelativemotionbetweenamagnetand
thecoil
8. “Alcoholsandglucosecontainhydrogenbutarenottreatedasacids”
a. False
b. Noplausibleexplanation
c. Thesetwoareexceptions
d. True
OR
Whathappenswhentwodropsofphenolphthaleinareaddedtoadilutesolutionof
NaOH?
a. solutionturnscolourless
b. solutionturnsred
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c. solutionturnsorange
d. solutionturnspink
9. Inafoodchain,thethirdtrophiclevelisalwaysoccupiedby
a. Producers
b. Decomposers
c. Herbivores
d. Carnivores
10. Whatwillhappenifdeerismissinginthegivenfoodchain?,Grass Deer Tiger.
a. Tigerwillstarteatinggrass.
b. Thepopulationofgrasswilldecrease.
c. Thepopulationoftigerwilldecreaseandthepopulationofgrasswillincrease.
d. Thepopulationoftigerwillincrease.
11. Whichofthepairsofelementsaremembersofthesamegroup?
A.NaandK
B.ArandCl
C.MgandCa
D.OandS
a. Allofthese
b. BandConly
c. A,CandD
d. AandDonly
12. Matchthefollowingwiththecorrectresponse:
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(1)Electrolyticreduction (A)Sodium
(2)Electrolyticrefining (B)Zinc
(3)Reductionwithcarbon (C)Impurecopper
(4)Reductionwithaluminium (D)Chromium
a. 1-C,2-B,3-D,4-A
b. 1-A,2-C,3-B,4-D
c. 1-B,2-D,3-A,4-C
d. 1-D,2-A,3-C,4-B
13. Assertion:PropenereactswithHBrtogiveisopropylbromide.
Reason:AdditionofBr2toalkenetakesplaceatthefasterrateinthepresenceof
ionizingsubstance.
a. BothassertionandreasonareCORRECTbut,reasonisNOTTHECORRECT
explanationoftheassertion.
b. AssertionisINCORRECTbut,reasonisCORRECT.
c. BothassertionandreasonareCORRECTandreasonistheCORRECTexplanationof
theassertion.
d. AssertionisCORRECTbut,reasonisINCORRECT.
14. Assertion:Whenthelengthofawireisdoubled,thenitsresistancealsogetsdoubled.
Reason:Theresistanceofawireisdirectlyproportionaltoitslength.
a. AssertionisINCORRECTbut,reasonisCORRECT.
b. BothassertionandreasonareCORRECTandreasonistheCORRECTexplanationof
theassertion.
c. BothassertionandreasonareCORRECTbut,reasonisNOTTHECORRECT
explanationoftheassertion.
d. AssertionisCORRECTbut,reasonisINCORRECT.
SectionB
15. Withthehelpofachemicalequation,explainhowasoda-acidfireextinguisherhelps
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inputtingoutafire.
16. Identifythesubstanceoxidizedandsubstancereducedinthefollowingreaction.
Writetheionicequationforthesubstanceoxidizedandreduced.
H2(g)+Cl2(g) 2HCl(g)
OR
WhathappenstolimewaterwhenCO2gasisbubbledthroughitinexcess?
17. Whydoyouthinkthenoblegasesareplacedinaseparategroup?
18. Whatchangestakeplaceasbloodentersthekidneytubule?
OR
i. Transportoffoodinplantsrequireslivingtissuesandenergy.Justifythis
statement.
ii. Namethecomponentsoffoodthataretransportedbythelivingtissues.
19. Apersonwithmyopiceyecannotseeobjectsbeyond1.2mdistinctly.Whatshouldbe
thetypeofthecorrectivelensusedtorestorepropervision?
20. Differentiateheritableandnon-heritablevariations.
21. Representschematicallythepathofareflexaction.
22. AmagneticcompassneedleisplacedintheplaneofpapernearpointAasshownin
figure.Inwhichplaneashouldastraightcurrentcarryingconductorbeplacedso
thatitpassesthroughAandthereisnochangeinthedeflectionofthecompass?Under
whatconditionisthedeflectionmaximumandwhy?
23. Supposeyourparentshaveconstructedatworoomhouseandyouwantthatinthe
livingroomthereshouldbeaprovisionofoneelectricbulb,oneelectricfan,a
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refrigeratorandaplugpointforappliancesofpowerupto2kilowatts.Drawacircuit
diagramshowingelectricfuseandearthingassafetydevices.
24.
i. Whatisthevisiblespectrum?
ii. Whyisredusedasthestoppinglightattrafficsignals?
iii. Twotriangularglassprismsarekepttogetherconnectedthroughtheirrectangular
side.Alightbeamispassedthroughonesideofthecombination.Willtherebeany
dispersion?Justifyyouranswer.
OR
i. Namethesphericalmirrorusedas:
a. shavingmirror
b. Rearviewmirrorinvehicles
c. Reflectioninsearch-light.
ii. Writeanythreedifferencebetweenarealandavirtualimage.
SectionC
25. Howwillyougetmetalfromconcentratedore?
26. Explainthemechanismofthecleansingactionofdetergents.
27. Listthestepsofpreparationofatemporarymountofaleafpeeltoobservestomata.
28. DescriberegenerationinPlanaria.
OR
Givereasons:
i. Placentaisextremelyessentialforfoetaldevelopment.
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ii. Blockingofvasdeferenspreventspregnancy.
iii. Windactsasapollinatingagent.
iv. Useofcondomspreventspregnancy.
v. BlockingofFallopiantubespreventspregnancy.
29. Redrawthecircuitputtinganammetertomeasurethecurrentthroughtheresistors
andvoltmetertomeasurethepotentialdifferenceacross12Ωresistor.whatwouldbe
thereadingintheammeterandthevoltmeter?
30. Howaretheimagesformedwhenanobjectismovedfrominfinitytotheconvexlens?
OR
i. Definefocallengthofasphericallens.
ii. Adivergentlenshasafocallengthof30cm.Atwhatdistanceshouldanobjectof
height5cmfromtheopticalcentreofthelensbeplaced,sothatitsimageis
formed15cmawaythelens?Findthesizeoftheimagealso.
iii. Drawaraydiagramtoshowtheformationofimageintheabovesituation.
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CBSEClass10Science
SamplePaper02(2019-20)
Answer
SectionA
1. ThebreakingandmakingofbondsinchemicalreactioniscalledasChemical
Bonding.
2. Givenelementsbelongtothesameperiod.Since,onmovingfromlefttoright,size
decreasesduetoincreaseinnuclearcharge.Duetothis,thetendencytoloseelectrons
decreasesalongtheperiod.Hence,themetalliccharacterofelementsalsodecreases.
Decreasingorderofmetalliccharacterofmetalsfollowstheorder:
Thus,Gapossessesmaximummetalliccharacter.
3. i. Non-renewableresourcesarethosefoundinsidetheearth,andtheytook
millionsofyearstoform.
ii. Thefiveexamplesofnon-renewableenergysourcesarefossilfuels,oil,natural
gas,andcoalandnuclearenergy.
iii. Carbonisthemainelementinfossilfuels.
iv. Combustionoffossilfueldoesn’tleadtothedestructionofwildlifehabitat.
4. a. Theroleofaxonistoconducttheactionpotentialtothesynapticterminal.
b. Theelectricalimpulsetravelsformthedendritetothecellbody,thenalongthe
axontoitsend.
c. Acetylcholinereleasedattheendofaxontotransmitthesignaltotheother
neuron.
d. (i)Electricalsignal
5. (a)increase,Explanation:AccordingtoSnell’slaw,ratioofthesineoftheangleof
incidencetothesineoftheangleofrefractionisalwaysconstantforagivenpairof
media.Therefore,iftheangleofincidenceincreases,theangleofrefractionalso
increasesproportionallytotheincreaseofincidence.
OR
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(c)arerelaxedandlensbecomesthinner,Explanation:Whentheciliarymusclesare
relaxed,theeyelensbecomesthin,thefocallengthincreases,andthedistantobjects
areclearlyvisibletotheeyes.
6. (c)Alloftheabove,Explanation:Disadvantagesofconstructionofdamsare:
Environmentalproblems:Theconstructionofdamsacrossriversleadsto
deforestation,whichresultsinthelossofbiodiversity.Thiscreatesadisturbancein
thenaturalecosystem.
Socialproblems:Theconstructionofdamsinvolvesthebuildingoflargereservoirs.In
somecases,constructingareservoirmayresultinthefloodingofnearbytownsand
villages.Alargenumberofpeoplearedisplacedasadirectconsequenceofthe
constructionofreservoirs.Insuchcases,thegovernmentrehabilitatesthepeopleof
theseareas,whichinitselfisahugetask.
Economicproblems:Theconstructionofdamsrequireshugeamountsofmonetary
investments.Adamdoesnotbecomeprofitableuntilitstartsgeneratingelectricity.
Asaresultofalltheseproblems,thereisastrongoppositiontotheconstructionof
largedams.TheoppositiontotheconstructionoftheTehridamovertheriverGanga
andtheNarmadaBachaoAndolan(aprotestagainsttheproposedincreaseintheheightofthe
SardarSarovarDamovertheriverNarmada)areexamplesofsuchopposition
7. (d)producinginducedcurrentinacoilbytherelativemotionbetweenamagnetand
thecoilExplanation:Whenastraightcoilandamagnetaremovedrelativetoeach
other,acurrentisinducedinthecoil.Thisphenomenonisknownaselectromagnetic
induction.
8. (d)True,Explanation:Thisistruethatalcoholsandglucosecontainhydrogenionsin
thembuttheydonotdissociatetoproducehydrogenionsandhenceareunableto
showacidicbehaviour.
OR
(d)solutionturnspink,Explanation:Phenolphthaleinisanacidbaseindicatorthatis
pinkinbasicsolutionsandcolourlessinacidicsolutions.NaOHisbasicinnature,so
whentwodropsofphenolphthaleinareaddedtoadilutesolutionofNaOHit’scolour
turnpink.
9. (d)Carnivores,Explanation:Carnivores
10. (c)Thepopulationoftigerwilldecreasesandthepopulationofgrasswillincrease.
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Explanation:Ifdeerismissingfromthegivenfoodchain,thepopulationoftigerwill
decreaseandthegrowthofgrasswillincrease.Amissinglinkinafoodchainwill
createanimbalanceintheecosystem.
11. (c)A,CandD,Explanation:SodiumandPotassiumarethegroup1elementsasthey
have1valenceelectronintheiroutermostshells.
MagnesiumandCalciumaregroup2elementsastheyhave2valenceelectronsin
theiroutermostshells.
SulphurandOxygenaregroup6elements.
12. (b)1-A,2-C,3-B,4-D,Explanation:Highlyreactivemetalslikesodium,whichcannotbe
obtainedbeextractedbyreducingtheiroxideswithcarbon,areobtainedbyelectrolysisof
theirchlorides(electrolyticreduction)inmoltenstate.Electrolyticrefiningisusedfor
refiningimpurecopper.Zincoxidecanbereducedwithcarbon(orcoke).Chromiumcanbe
obtainedfromitsoxideorebyreductionwithaluminiumpowder.
13. (a)BothassertionandreasonareCORRECTbut,reasonisNOTTHECORRECT
explanationoftheassertion.Explanation:BothassertionandreasonareCORRECT
but,reasonisNOTTHECORRECTexplanationoftheassertion.
14. (b)BothassertionandreasonareCORRECTandreasonistheCORRECTexplanationof
theassertion.Explanation:BothassertionandreasonareCORRECTandreasonisthe
CORRECTexplanationoftheassertion.
SectionB
15. Soda-acid fire extinguisher contains sodium bicarbonate and sulphuric acid,which
arepresentinseparatecontainersinsidetheextinguisher.Whentheknobofthefire
extinguisher is pressed, the sulphuric acidmixeswith sodiumbicarbonate solution
andalotof gasisproduced.
Carbondioxidegasformsablanketoverthefireandcutsoffthesupplyofairtothe
burningsubstanceandthefirestops.
16. H2(g)+Cl2(g) 2HCl(g)
a. Substanceoxidized,H2
H2 2H++2e
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[SubstancegettingoxidizedisH2]
b. Substancereduced,Cl2
Cl2+2e 2Cl
[SubstancegettingreducedisCl2]
OR
Whencarbondioxideispassedinexcessinlimewatertheninitiallyitturnsmilky
duetotheformationofaprecipitateofcalciumcarbonate,followedbyformationofa
clearsolutionintheend.
17. Nobelgasesareplacedinseparategroupsbecauseofthefollowingreasons
(i)DuringtheperiodwhenMendeleevdiscoveredhisperiodictablenobelgaseswere
notdiscovered.Whennobelgaseswerediscoveredscientistsgavetheconclusionthat
nobelgasesecouldbeplacedattheextremerightoftheperiodictable.
(ii)Theoutermostshellcontainseightelectronwhichisknownasoctate.(exceptional
case:Heliumwhichcontainstwoelectronsinthisvalenceshell.Thus,itisknownas
Duplet)
(iii)Nobelgasesshowsimilarchemicalpropertiesastheno.ofelectronsinthe
outermostshellissame.Hencetheyhavesimilarchemicalproperties
(iv)Theirvalencyis0.
18. Asthebloodenterskidneytubules,itisfilteredintheglomerulus.Thenephricfiltrate
thusentersthebodyoftubule,theusefulsubstancesdiffusebackintokidneyandthe
wastesaltsalongwithexcesswaterreachesthecollectingtubule.
OR
i. Foodistransportedbysievetubes(phloem)attheexpenseofATP.Asphloemis
largelycomposedoflivingcellsthus,itshowsthatfoodtransportrequiresliving
tissuesandenergy.
ii. Componentsoffoodthataretransportedbythelivingtissuesare:
a. Photosyntheticproductsorsucrose
b. Aminoacids.
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19.
Personshouldwearspectsofpower-0.825D.
20.
Heritablevariations Non-heritablevariations
1)Thesevariationsaffectthegermcells. 1)Theyaffectsomaticcells.
2)Theyaretransmittedtothenextgeneration.2)Theyarelostwiththedeathof
organisms.
3)Theyareproducedbynewcombinationof
characters,
crossingover,changeinnumberof
chromosomes,radiationsandchemicals.
3)Theyareproducedbythreetypes
offactors:environment,
useanddisuseoforgansand
consciousefforts.
4)Theyarealsocalledgerminalvariations.4)Theyaretermedassomatic
variations.
21.
22. Whenthemagneticfieldanddirectionofelectriccurrentareinthesameplane,there
wouldbedeflectioninthecompass.Formaximumdeflection,magnaticfieldand
directionofcurrentshouldbeinmutuallyperpendicularplane.So,fornodeflection,
conductorsshouldbekeptparalleltothemagneticcompass.Formaximumdeflection,
itshouldbeplacedperpendiculartothecompass.
23. Thecircuitdiagramshowingtheelectricfuseandearthingassafetydevicesisas
follows:
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24. i. Visiblespectrumisthebandofcolouredcomponentsofawhitelightbeam.
ii. Redlightisscatteredtheleastbyairmoleculesandhaslongerwavelength.It
travelsthelongestdistance.
iii. Thegivensetupwillbehavelikeaglassslab,resultinginrecombinationofthe
sevencolourstoproducewhitelight.
OR
i. a)Shavingmirror-Concavemirror
b)Rearviewmirror-Convexmirror
c)Reflectioninsearch-lights-Concavemirror.
ii. Thethreedifferencesare:
a)Realimagecanbeobtainedonscreenbutavirtualimagecannotbeobtained.
b)Reflected/Refractedraysactuallymeetwheretherealimageisformedwhilefor
virtualtheyonlyappeartomeet.
c)ARealimageisalwaysinvertedwhilethevirtualimageisalwayserect.
SectionC
25. Extractionofthemetalfromtheconcentratedore.Themetalisextractedfromthe
concentratedorebythefollowingsteps:
(i)Conversionoftheconcentratedoreintoitsoxide.Thisisusuallydoneby
calcinationandroastingprocess.Themethoddependsuponthenatureoftheore.A
carbonateoreisconvertedintooxidebycalcinationwhileasulphideoreisconverted
intooxidebyroasting.
(ii)Conversionofoxidetometalbyreductionprocess.
(i)Conversionoforeintometaloxide:Itcanbedonebytwomethods
(a)Calcination:Itistheprocessofheatingtheconcentratedoreintheabsenceofair.
Thecalcinationprocessisusedtoremovedvolatileimpurities,waterfromthe
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hydratedoresandtoconvertcarbonateoresintometaloxide.
Forexample:
(i)Zincoccursaszinccarbonateincalamine(ZnCO3).Theoreiscalcinated(heated
strongly)intheabsenceofairtoconvertittozincoxide.Duringcalcination,carbon
dioxideisexpelled.
ZnCO3 ZnO + CO2
Zinccarbonate(Calamineore) (Zinc.Oxide)
(ii)AluminiumoccursasAl2O3.2H2Oinitsbauxiteore.Whenthebauxiteoreis
calcined,watervapoursareexpelledandanhydrousaluminiumoxideisobtained.
Al2O3.2H2O Al2O3 + 2H2O
BauxiteOre AluminiumOxide
b)Roasting:Itistheprocessofheatingtheconcentratedorestronglyinthepresence
ofexcessair.Thisprocessisusedforconvertingsulphideorestometaloxide.
Forexample,zincoccursassulphideinzincblende(ZnS).Itisstronglyheatedin
excessofairwhenitformszincoxideandsulphurdioxidegasisexpelled.
2ZnS+3O2 2ZnO + 2SO2
Zincsulphide(Zincblendeore) ZincOxide
ii)Conversionofmetaloxidetometal:Themetaloxideformedaftercalcinationor
roastingisconvertedintometalbyreduction.Someofthemethodscommonlyused
forthereductionofmetaloxidestometalsarediscussedbelow:
I)Reductionbyheatingintheair:Metalslowinthereactivityseriescanbe
obtainedfromtheiroxidesbyheatinginair.Forexample,mercuryisobtainedfrom
cinnabar(HgS)orebythismethod.Themethodinvolvesthefollowingsteps:
i)Theconcentratedmercuricsulphide(cinnabaror)isroastedinairwhenmercuric
oxideisformed.
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2HgS + 3O2 2HgO + 2SO2
Mercuricsulphide(Cinnabarore) Mercuricoxide
2HgO → 2Hg + O2
Mercuricoxide Mercuricmetal
ii)Mercuricoxideisheatedtoabout300oCanditdecomposestogivemercurymetal.
II)Chemicalreduction:Themetaloxidesfromcalcinationorroastingprocessesare
reducedtofreemetalbyusingchemicalagentslikecarbon,aluminium,sodiumor
calcium.
(a)Reductionwithcarbon:Theoxidesofmoderatelyreactivemetalslikezinc,
copper,nickle,tin,leadetc.canbereducedbyusingcarbonasreducingagent.Inthis
process,themetaloxideismixedwithcokeandheatedinafurnace.Carbonreduces
themetaloxidetofreemetal.
Fore.g.whenzincoxideisheatedwithcarbon,zincmetalisproduced.
ZnO + C Zn + CO
Zincoxide Reducingagent Zincmetal Carbonmonoxide
Similarly,leadisobtainedfromleadoxidebyheatingwithcarbon.
PbO + C → Pb + CO
Leadoxide Leadmetall
Cokeisverycommonlyusedasareducingagentbecauseitischeap.
(b)Reductionwithcarbonmonoxide:Metalscanbeobtainedfromoxidesby
reductionwithcarbonmonoxideinthefurnace.Forexample,ironisobtainedfrom
ferricoxidebyheatingwithcarbonmonoxide.
Fe2O3(s)+3CO 2Fe+3CO2
c)Reductionwithaluminium:Certainmetaloxidesarereducedbyaluminiumto
metals.Themethodisknownasaluminothermyorthermiteprocess.Forexample,
chromium,manganese,titanium,vanadiummetalsareobtainedbythereductionof
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theiroxideswithaluminiumpowder.
3MnO2 + 4Al 3Mn + 2Al2O3
Manganeseoxide Manganese
Cr2O3 + 2Al 2Cr + Al2O3
Chromiumoxide Chromium
Similarly,chromiumisobtainedbyheatingchromiumoxidewithaluminium
powder.
(d)Reductionbyelectrolysisorelectrolyticreduction:Theoxidesofactivemetals
arecommonlyextractedbytheelectrolysisoftheirfusedsaltsusingsuitable
electrodes.Thisisalsocalledeelctrolyticreduction.Theprocessofextractionof
metalsbyelectrolysisprocessiscalledelectrometallurgy.
Fore.g.,aluminiumoxideisverystableandaluminiumcannotbepreparedby
reductionwithcarbon.Itispreparedbytheelectrolysisofmoltenalumina(Al2O3).In
thisprocesspurealuminaisdissolvedinmoltencryolite(Na3ALF6)inanirontank
linedwithcarbon.Duringelectrolysis,thealuminiumions,Al3+arereducedat
cathode(bytheelectrons)toformaluminium.
Al3+ + 3e- → Al
Aluminiumion(frommoltenalumina) Aluminium(Atcathode)
Duringelectrolyticreductionofmoltensalts,themetalsarealwaysproducedatthe
cathode(negativeelectrode).
26. Thecleansingactionofsoapsanddetergentsfollowsthesameprinciple:Soapsand
detergentsconsistoflargehydrocarbontailswithanegativelychargedhead.The
hydrocarbontailsarehydrophobicandnegativelychargedheadishydrophilic.In
solution,watermolecules(beingpolar)aqueous,surroundtheionsandnotthe
organicpartofthemolecule.
Whenasoapordetergentisdissolvedinwater,themoleculesaggregatetogetheras
clusters,calledmicelles.Thetailsstickinwardsandtheheadsoutwards.
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Mechanismofcleansingaction:Thehydrocarbontailattachesitselftooilydirt.When
waterisagitated,theoilydirttendstoloosenfromthedirtysurfaceanddissociates
intofragmentsandothertailstosticktooil.Thesolutionnowcontainssmallglobules
ofoilsurroundedbysoapordetergentmolecules.Thenegativelychargedheads
presentinwaterpreventthesmallglobulesfromcomingtogetherformingaggregates.
Thus,theoilydirtisremovedfromtheobject.
27. Thestepsare:
i. Removeahealthyleaffromthepottedplant.
ii. Removeapartofthepeelfromthelowersurfaceoftheleaf.Thepeelcanbe
removedbyfoldingtheleafoverandgentlypullingthepeel-apartusingforceps.
Placethepeelinawatchglasscontainingwater.
iii. Addsafranintothewatchglasstostainthepeellightly.
iv. After2-3minutestakeouttheandplaceisonacleanslide.
v. Putadropofglycerineoverthepeelandplaceacleancoverslipgentlyoveritwith
thehelpofaneedle.
vi. Removetheexcessstainandglycerinewiththehelpofblottingpaper.
vii. Observetheslideunderthelow-powerandhigh-powermagnificationsofthe
compoundmicroscope.
28. RegenerationinPlanaria:WhentheanteriorendofPlanariaiscutalongthelength
intotwomoreparts,eachpartdevelopsintoanewhead,resultinginamany-headed
planaria.
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Ifthebodyiscutintothree,fourormorepieces,eachpieceregeneratesthemissing
parts.Anoteworthyobservationinthiscaseisthatapiecefromthemiddlealways
regeneratesaheadtowardsitsanteriorsideandtailtowardsitsposteriorside.In
otherwords,eachpiecemaintainsitsoriginalpolarity.Apossibleexplanationofthis
factisthatinPlanaria,themetabolicactivityandhencecapacityforregeneration,is
thegreatestattheanteriorend,graduallydecreasesposteriorlyandisminimumat
theposteriorend.Correspondingly,theanteriorendofeachpiece,havinggreater
metabolicactivity,regenerativeanteriorpartofthebodyandtheposteriorend
remainassuch.
OR
i. Placentaisatemporaryorganwhichisextremelyessentialforfoetaldevelopment
becauseithelpsinnutrition,respiration,excretion,etc.,ofthefoetusthroughthe
maternalsupply.Babyconnectswithplacentaviaumblicalcord.
ii. Blockingofvasdeferensisknownasvasectomywhichpreventspassageof
sperms,hence,thereisnofertilisationthusitpreventspregnancy.
iii. Anemophilyorwindpollinationisaformofpollinationwhere,windactsasa
pollinatingagentbecauseithelpsintransferofpollengrainsfromantherto
stigmaofaflower.e.g.wheat,ricecorn.
iv. Condomsasphysicalbarrier,whichprevententryofspermsintovagina,hence
preventpregnancy.
v. IfFallopiantubeisblockedsurgically,whichisbetterknownbythename
tubectomy,spermandeggdonotmeetandfuseandfertilisationdoesnottake
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place.
29. Modifiedcircuitisasshown.Since5Ω,8Ωand12Ωareinseries,thereforethetotal
resistanceinseries.
Rs=R1+R2+R3=5+8+12=25Ω
CurrentthroughcircuitI=
Readingofammeter=0.24A
=I.R.=0.24 12
=2.88Ω
30. ObjectatInfinity.Whenobjectisatinfinity,arealimageisformedatFontheother
sideofthelens
Objectatinfinity.ImageatFontheothersideoflens.
Howeveriftheraysareparalleltothemselvesbutnotparalleltoprincipalaxis,then
theseraysafterrefractionwillformimageatfocusF'andnotatprincipalfocusF.
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Objectatinfinity,raysparalleltothemselvesbutnotparalleltoprincipalaxis.Image
isformedatF',thefocusontheothersideoflens.Objectbeyond2F.Whentheobject
isbeyond2F,areal,inverted,diminishedimageisformedbetweenFand2F.
Objectbeyond2F,real,inverted,diminishedimagebetweenFand2F.Objectat2F.
Whentheobjectisat2F,areal,invertedimageofthesamesizeisformedontheother
sideofthelensat2FasgiveninFig.
Objectat2F,imageat2Fontheothersideofthelens.Imageisofsizesameasthatof
theobject.WhentheobjectisbetweenFand2F,itsreal,inverted,magnifiedimageis
formedontheothersideoftheconvexlensasshowninfig.
ObjectbetweenFand2Freal,inverted,magnifiedimageisformedbeyond2Fonthe
othersideoflens.
ObjectatF.Whenobjectisplacedprincipalfocus,areal,inverted,veryhighly
magnifiedimageisformedatinfinity.
ObjectatF,averyhighlymagnified,real,invertedimageisformedatinfinity.
ObjectbetweenFandC.Whenanobjectisplacedbetweenprincipalfocusandoptical
centreofthelens,virtual,erect,magnifiedimageisformedonthesamesideofthe
lens.
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ObjectbetweenFandC;avirtual,erect,magnifiedimageisformedonthesameside.
OR
i. Thedistancebetweenthefocusandopticalcentreoflensiscalledfocallengthof
lens.
ii. Given
f=-30cm,v=-15cm,u=?,h0=5cm
m=
iii.