Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

For an electron , if the uncertainty in velocity isv ,the uncertainty in its position (x) is given by :

  • hm4πν

  • 4πhmν

  • h4πmv

  • 4πmhν


C.

h4πmv

According to Heisenberg's uncertainty principle

x.ph4π (p = mν)

x. mvh4π

x =h4πmv


2.

The enthalpy change (H) for the neutralisationof M HCl by caustic potash in dilute solution at298 K is :

  • 68 kJ

  • 65 kJ

  • 57.3 kJ

  • 50 kJ


C.

57.3 kJ

HCl(strongacid)+KOH(strongbase)neutralisationKCl + H2O

In this reaction , HCl is the strong acid and KOHis the base and it has been found that the heat ofneutralisation of a strong acid with a strong baseis always constant i.e. , 57.3 kJ .


3.

Orbital is :

  • circular path around the nucleus in which the electrons revolves

  • space around the nucleus where the probability of finding the electron is maximum

  • amplitude of electron wave

  • none of the above


B.

space around the nucleus where the probability of finding the electron is maximum

An atomic orbital is a three dimensional regionof definite shape around the nucleus where theprobability of finding the electron is maximum .Therefore , an atom has a both characteristicenergy and a characteristic shape .


4.

A radioactive sample is emitting 64 timesradiations than non-hazardous limit .If itshalf-life is 2 hours , after what time it becomesnon- hazardous ?

  • 16 h

  • 10 h

  • 12 h

  • 8 h


C.

12 h

We know ,

Nt = Nox12n

where Nt = amount left after expiry of 'n' half lives

No = initial amount

n = number of half lives elapsed

NtNo=12n

164=12n

126=12n

n = 6

Time taken (T) = t1/2 x n = 2 x 6 = 12 h


5.

A metal surface is exposed to solar radiations :

  • the emitted electrons have energy less than a maximum value of energy depending upon frequency of incident radiations

  • the emitted electrons have energy less than maximum value of energy depending upon intensity of incident radiations

  • the emitted electrons have zero energy

  • the emitted electrons have energy equal to energy of photons of incident light


A.

the emitted electrons have energy less than a maximum value of energy depending upon frequency of incident radiations

A metal surface is exposed to solar radiations ,the emitted electrons have energy less thanmaximum value of energy depending uponfreauency of incident radiations .


6.

Ionic compounds are formed most easily with :

  • low electron affinity , high ionisation energy

  • high electron affinity , low ionisation energy

  • low electron affinity , low ionisation energy

  • high electron affinity , high ionisation energy


B.

high electron affinity , low ionisation energy

An ionic bond is formed between an electropositive metal and a electronegative non metal .The electropositive metal converts into a cation ,while the electronegative non metal convertsinto a anion .

Thus the formation ofionic bond is favoured by

(I)Low ionisation potential of metal

(II)Greater valtie of electron affinity of nonmetal

(III)Higher value of lattice energy of theresulting ionic compound .


7.

The Ksp of Mg(OH)2 is 1 x 10-12 , 0.01 M Mg(OH)2will precipitate at the limited pH :

  • 3

  • 9

  • 5

  • 8


B.

9

Mg(OH)2Mg2+ + 2OH-

the solubility product Kspof

Mg(OH)2 = [Mg2+][OH-]2

1 x 10-12 = 0.01 [OH-]2

[OH-]2 = 1 x 10-10

[OH-] = 10-5

We know

[H+][OH-] = 10­-14

[H+][10-5]= 10-14

[H] = 10-14/10-5 = 10-9

pH = - log[H+] = - log 10-9 = 9


8.

Which of the following sequence is correct as perAufbau principle ?

  • 3s < 3d < 4s < 4p

  • ls < 2p < 4s < 3d

  • 2s < 5s < 4p < 5d

  • 2s < 5s < 4p < 5f


B.

ls < 2p < 4s < 3d

According to aufbau principle , "sub-shells arefilled with electrons in the increasing order oftheir energies , "i.e. , sub-shell of lower energywill be filled first with electrons .

Thus correct order is -

1s < 2s < 2p < 3s < 3p < 4s < 3d < 4p< 5s < 4d < 5p < 6s < 4f < 5d < 6p< 7s < 5f < 6d ... etc


9.

Which of the following transitions haveminimum wavelengths ?

  • n4  n1

  • n2  n1

  • n4  n2

  • n3  n1


A.

n4  n1

E =hcλor E1λ

Thus a decrease in wave length represents anincrease in energy Forn4n1transition .These are greater the. energy difference andlesser will be wavelength .Thus , forn4n1 transition has minimum wavelength .


10.

Equation of Boyle's law is :

  • dPP = -dVV

  • dPP = +dVV

  • d2PP = -dVdT

  • d2PP = +d2VdT


A.

dPP = -dVV

According to Boyle's law , "for a given mass of agas , at constant temperature the volume of a gasis inversely proportional to its pressure" .

V1P

or PV = constant

on differentiating the equation

d(PV) = d (constant)

= PdV + VdP =0

= VdP = - PdV

=dPP= -dVV