NEET Practice Questions (MCQs) with Answers & Solutions

(1)

Hydrogen is not a greenhouse gas. Greenhouse gases must contain different atoms that are able to vibrate in a specific pattern to absorb heat energy

Levels of peroxyacetyl nitrate and total oxidant at Riverside, Calif., November 13, 1967. Maximum concentration (58 ppb) of PAN measured to date occurred between 6:30 and 8:00 p.m. Total oxidant was above ad- verse level but did not reach an unusually high level for a "smoggy" day.

This is called photochemical smog...

(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

(d) All are covalent molecules. A covalent solid has atoms as constituent units at lattice points held together by covalent bonds.

(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

(a) The bcc structure has co-ordination no. of eight.

(a) Mass of one unit cell = V x d (V is volume, d is density) 

= a³ x d

Also, density = (n x at. mass) /(a³ x av.no.)

Mass of one unit cell = (a³ x n x at.mass) / (a³ x av.no.) = (n x at. mass )/(av.no.)

= 4x58.5 / 6.02 x 10²³ (n=4 for cubic shape)

=38.87 x 10^-23g

No. of unit cell in 1g = 1/38.87x10^-23 = 2.57 x 10²¹