Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

The dipole moment is minimum in

  • NH3

  • NF3

  • SO2

  • BF3


D.

BF3

BF3 has zero dipole moment


2.

Threshold frequency of a metal is 5 × 1013 s-1 upon which 1 x 1014s-1 frequency light is focused. Then the maximum kinetic energy of emitted electron is

  • 3.3 × 10-21

  • 3.3 × 10-20

  • 6.6 × 10-23

  • 6.6 × 10-20


B.

3.3 × 10-20

Following the conservation of energy principle,

Kinetic energy 12mev2 = h(v-v)

                    =(6.626 × 10-34) (1014s-1 - 5 × 1013 s-1)

                    =(6.626 x 10-34J s) (5 x 1013 s-1)             

                    =3.313 x 10-20J.


3.

Bond dissociation energy of CH4 is 360 kJ/mol and C2His 620 kJ/mol. Then bond dissociation energy of C-C bond is

  • 170 kJ/mol

  • 50 kJ/mol

  • 80 kJ/mol

  • 220 kJ/mol


C.

80 kJ/mol

Dissociation energy of methane = 360 kJ mol-1

Bond energy of C-H bond =3604=90 kJ

Bond energy of ethane,

1(C-C) 6 (C-H) =620 kJ/mol

(C-C) + 6 × 90 = 620

(C-C) + 540 = 62

C-C = 80 kJ mo1-1
Bond dissociation of C-C bond= 80 kJ moJ-1.

 


4.

pKa increases in benzoic acid when substituent "x" is bonded at para-position, then "x" is

  • -COOH

  • -NO2

  • -CN

  • -OCH3


D.

-OCH3

Larger the value of pKa smaller will be its acidity. Out of the four groups, -COOH, -NO2 and -CN are e- withdrawing which makes benzoic acid more acidic whereas -OCH3 is e- donating which reduces the acidity (makes H less easily available). pKa value increases if OCH3 is present at para-position of benzoic acid.


5.

KpKc for following reaction will be CO(g)+12 O2(g)CO2(g).

  • RT

  • 1RT

  • 1RT

  • RT2


C.

1RT

ng=np-nr = 1-32

ng= -12. Hence K= Kc(RT)-1/2

KpKc=1(RT)1/2=1RT


6.

In Bohr's Orbit, nh2π indicates

  • Momentum

  • Kinetic energy

  • Potential energy

  • Angular momentum


D.

Angular momentum

Angular momentum = mνr= nh2π

 

 


7.

Which has the highest pH?

  • CH3COOK

  • Na2CO3

  • NH4Cl

  • NaNO3


B.

Na2CO3

NH4Cl solution is acidic, its pH < 7. NaNO3 solution is neutral, its pH = 7. CH3COOK and Na2CO4solutions are basic their pH > 7. But Na2CO3 solution is more basic, its pH > pH of CH3COOK solution.


8.

Arrange the following gases in order of their critical temperature.
NH3, H2O, CO2, O2

  • NH> H2O > CO> O2

  • O> CO> H2O > NH3

  • H2O > NH> CO> O2

  • CO>O>H2O > NH3


C.

H2O > NH> CO> O2

Greater are the intermolecular forces of attraction, higher is the critical temperature.


9.

At 60° and 1 atm, N2O4 is 50% dissociated into NO2 then KP is

  • 1.33 atm

  • 2 atm

  • 2.67 atm

  • 3 atm


B.

2 atm

             N2O4  2NO2

Initially     1          0

At equili.  1- α      2α

N2O4 is 50% dissociated, so α =12

Kp=pNO22pN2O4=(2×12)2(1-12)=2 atm


10.

At equilibrium which is correct?

  • G = 0

  • S = 0

  • H = 0

  •  G°= 0


A.

G = 0

In unfavorable reaction have Delta G values that are positive (also called endergonic reaction). When Delta G for reaction is zero, a reaction is said to be at equilibrium. Equilibrium does not mean equal concentrations. If the Delt G is zero, there is no net change in A and B, as the system is at equilibrium.