Physics MCQs for NEET — Practice Questions with Answers

(C)  $\mathrm{V} \mathrm{\alpha } \mathrm{n}$ at same temperature and Pressure.

(A). Low ionisation energies of potassium and caesium.

(c) Doping of NaCl with 10^-4 mol % of SrC_l2 means, 100 moles of NaCl are doped with 10^-4  mol of SrCl₂.

.^.. 1 mol of NaCl is doped with

                      SrCl₂ = 10^-4/100 = 10^-6 mole

 As each Sr²⁺ ion introduces one cation vacancy.

.^.. Concentration of cation vacancies

                             = 10^-6 mol/mol of NaCl

                             = 10^-6 x 6.023 x 10²³ mol^-1

                             = 6.023 x 10¹⁷ mol^-1

(C) For bcc if edge length is a, then 

r_Cs+ + r_Cl- = ($\sqrt{3}$/2)*a

(b) The conductance order of metals is 10⁶ to 10⁸ ohm^-1 cm^-1.

(D) Volume of atoms in cell = 4/3 $\pi$r³ x n (n =4 for fcc)

=  4/3 x $\pi$r³ x 4 = 16/3 $\pi$r³

(c) A unit cell of CsCl having bcc structure consists of 8 atoms at the corner and one atom at centre.

Thus, no. of Cl^- = 8x1/8 =1 and no. of Cs⁺ =1x1=1

Thus, no. of CsCl unit per unit cell = 1

(d) The n-type semiconductors are obtained when Si or Ge are doped with elements of group 15, eg, arsenic (As), while p-type semiconductors are obtained when Si or Ge are doped witlh traces of elements of group 13, ie, indium (In), boron (B).

Note : The conductivity of semiconductors increases with rise in temperature

the gas (preferably hydrogen or helium) is enclosed in a glass or fused-quartz bulb connected to a mercury manometer.

The NCERT text states: 'Bohr’s model was also unable to explain the splitting of spectral lines in the presence of magnetic field (Zeeman effect) or an electric field (Stark effect).' Options 1, 2, and 4 are phenomena that Bohr's model successfully explained for hydrogenic atoms.