Subject

Chemistry

Class

NEET Class 12

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 Multiple Choice QuestionsMultiple Choice Questions

1.

For the Paschen series the values of n1 and nin the expression E =Rhc1n12-1n22 are

  • n1= 1, n2 = 2, 3, 4, ...

  • n1= 2, n2 = 3, 4, 5,...

  • n1= 3, n= 4,5,6,...

  • n1= 4, n2 = 5,6,7,...


C.

n1= 3, n= 4,5,6,...

Paschen series is the third series of hydrogen spectrum and lies in the infrared region, therefore for this series, n1 = 3 and n> n1,ie, 4, 5, 6,....


2.

The equilibrium constant (K) of a reaction may be written as

  • K = e-G/RT

  • K =e-G°/RT

  • K = e-H/RT

  • K = e-H°/RT


B.

K =e-G°/RT

Gibbs free energy (G°) is related with equilibrium constant (K) as          G° = -RT ln K    - G°RT = ln K            K = e-G°RT


3.

Which of the following will decrease the pH of  a 50 mL solution of 0.01 M HCl?

  • Addition of 5 mL of 1 M HCl

  • Addition of 50 mL of 0.01 M HCl

  • Addition of 50 mL of 0.002 M HCl

  • Addition of Mg


B.

Addition of 50 mL of 0.01 M HCl

Millimoles of 50 mL of 0.01 M HCl
             = 50 x 0.01 M = 0.5
pH of the solution =-log (0.5) = 0.3010

(a) On adding 5 mL of 1 M HCl,
           Concentration of the resultant solution

         =50 × 0.01+ 5 ×150+5=0.1

     :. pH of the solution = -log (0.1) = 1

(b) On adding 50 mL or 0.01 M HCl,
       Concentration of the resultant solution

         =50 x 0.01 + 50 x 0.0150 + 50= 0.01

  :. pH of the solution = -log (0.01) = 2

(c) On adding 50 mL of 0.002 M HCl,
       concentration of the resultant solution

       =50 ×0.01+ 50 x 0.00250 +50= 6×10-3

:. pH of the solution = -log (6 x 10-3)= 2.22

(d) On adding Mg,

    Mg +2HCl  MgCl2 + 2H+  Since, pH  1[H+]:. In this case pH decreases.


4.

An organic compound made of C, H and N contains 20% nitrogen. Its molecular weight is

  • 70

  • 140

  • 100

  • 65


A.

70

Atomic mass of nitrogen= 14
Since the compound contains C, H and N, at
least one N atom must be there in the molecule.

          20% N =14100 % =1420 × 100 = 70

:. The minimum molecular weight of the organic  compound = 70.


5.

For the reaction  SO2 + 12O2  SO3 , if we write Kp = Kc(RT)x, then x become

  • -1

  • -12

  • 12

  • 1


B.

-12

In the relation, Kp= Kc(RT)x,                   x= np-nrFor the reaction,    SO2(g) + 12O2(g) SO3(g)            x = 1 - 1 +12 =-12


6.

1 mole of photon, each of frequency 2500 s-1, would have approximately a total energy of

  • 10 erg

  • 1 J

  • 1 eV

  • 1 MeV


A.

10 erg

Frequency of one photon = 2500 s-1
:. Frequency of 1 mole of photon
               = 6.023 x 1023 x 2500 s-1

Total energy of 1 mol of photon, E=             = 6.626 × 10-34Js ×6.023 ×1023× 2500 s-1             = 9.97 × 10-7J 10 erg

 


7.

Hybridisation of central atom in NF3 is

  • sp3

  • sp

  • sp2

  • dsp2


A.

sp3

Number of hybrid orbitals = number of σ bonds + number of lone pairs

       3σ bonds + 1 lone pair = 4

.:. Hybridisation of N is sp3 and geometry of the molecule is pyramidal.


8.

Equal volumes of molar hydrochloric acid 'and sulphuric acid are neutralized by dilute NaOH solution and x kcal and y kcal of heat are liberated respectively. Which of the following is true ?

  • x = y

  • x =y/2

  • x = 2y

  • none of these


B.

x =y/2

Heat of neutralisation= Heat of formation of water (1 mol).

HCl + NaCl  NaCl + H2O;                               H =-xor H+1mol + OH- 1mol H2O;                                          H = xH2SO4 + 2NaOH Na2SO4 + 2H2O ;               H = -yor 2H++ 2OH-2H2O;                                      H =-yH+ + OH-  H2O;                                             H =-y2  H = H  x =y2


9.

The second law of thermodynamic says that in a cyclic process

  • work cannot be converted into heat

  • heat cannot be converted into work

  • work cannot be completely converted into heat

  • heat cannot be completely converted into work


D.

heat cannot be completely converted into work

Second law of thermodynamics states that in a cyclic process heat cannot be converted completely into work because attainment of 0 K temperature is impossible.


10.

Under which of the following conditions is the relation H =E + PV valid for a closed system ?

  • Constant pressure

  • Constant temperature

  • Constant temperature and pressure

  • Constant temperature, pressure and composition


A.

Constant pressure

At constant pressure,

  p =0H=E +pV is valid.