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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



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



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



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:



(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



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



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.



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.



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



(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.



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



[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.



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:



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



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.



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



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.



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.



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



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.



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.



ObjectbetweenFandC;avirtual,erect,magnifiedimageisformedonthesameside.

OR

i. Thedistancebetweenthefocusandopticalcentreoflensiscalledfocallengthof

lens.

ii. Given

f=-30cm,v=-15cm,u=?,h0=5cm

m=

iii.
