Assertion : In NaCl crystal each Na ion is touching 6 $C{l}^{‐}$ ions but these $C{l}^{‐}$ ions do not touch each other.

Reason : The radius ratio roe $r_{Na}/r_{Cl-}$ is greater than 0.414, required for exact fitting.

1. If both the assertion and the reason are true and the reason is a correct explanation of the assertion
2. If both the assertion and reason are true but the reason is not a correct explanation of the assertion
3. If the assertion is true but the reason is false
4. If both the assertion and reason are false

Assertion : The ratio of $Z{n}^{2+ }$and F- per unit cell of ZnS and $Ca{F}_2$ is 1:2. 

Reason : In ZnS $Z{n}^{2+}$ ions occupy alternate tetrahedral voids and in $Ca{F}_2$ F- ions occupy all the tetrahedral voids of FCC unit cell.

Sodium metal crystallizes in bcc lattice with cell edge $=4.29 \stackrel{0}{A}$. The radius of sodium atom will be-

(1) 1.50 $\stackrel{0}{A}$                                                 

(2) 1.86  $\stackrel{0}{A}$

(3) 2.80 $\stackrel{0}{A}$                                               

(4) None of these 

The space lattice of graphite is

1. Cubic                                     

2. Tetragonal

3. Rhombic                                 

4. Hexagonal

The edge length of the cube is 400pm. Its body diagonal would be-

(1) 500 pm                                         

(2) 693 pm

(3) 600 pm                                           

(4) 566pm

A metallic element exists as a cubic lattice. Each edge of the unit cell is 2.88 $\stackrel{0}{A}$. The density of the metal is 7.20 g $c{m}^{-3}$. How many unit cell will be present in 100 g of the metal -

(1) $6.85\times {10}^2$                             

(2) $5.82\times {10}^{23}$

(3) $4.37\times {10}^5$                             

(4) $2.12\times {10}^6$

Iron crystallizes in a b.c.c. system with a lattice parameter of 2.861 $\stackrel{0}{A}$. Calculate the density of iron in the b.c.c. system (Atomic weight of Fe = 56, $N_A=6.02\times {10}^{23}mo{l}^{-1}$)

(1) 7.92g $m{l}^{-1}$                                   

(2) 8.96g $m{l}^{-1}$

(3) 2.78g $m{l}^{-1}$                                     

(4) 6.72g $m{l}^{-1}$

An alloy of copper, silver, and gold is found to have copper constituting the ccp lattice. If silver atoms occupy the edge centers and gold is present at the body center, the alloy has a formula-

(1) $C{u}_{4}A{g}_{2}Au$                               

(2) $C{u}_{4}A{g}_{4}Au$

(3) $C{u}_{4}A{g}_{3}Au$                               

(4) $CuAgAu$

Frenkel defect is not found in the halides of alkali metals because alkali metals have

1. high electropositivity

2. high ionic radii

3. high reactivity

4. ability to occupy interstitial sites

Iodine crystals are classified as-

1. Metallic solids.                                  

2. Ionic solids.

3. Molecular solids .                                 

4. Covalent solids.