Potassium fluoride has NaCl type structure. What is the distance between K⁺ and F^- ions, if edge length of unit cell is 'a'.

• $\frac{\mathrm{a}}{2}$

• $\frac{\mathrm{a}}{4}$

• 2a

• 4a

22.

The flame colours of metal ions are due to

• Schottky defect

• Frenkel defect

• Metal excess defect

• Metal deficient defect

An alloy of copper, silver and gold is found to have copper atom constituting the ccp lattice. If silver atom occupy the edge centres and gold atom is present at body centred, the alloy has a formula

• Cu₄Ag₂Au

• Cu₄Ag₄Au

• Cu₄Ag₃Au

• CuAgAu

A metal has bee structure and the edge length of its unit cell is 3.04 $\stackrel{°}{\mathrm{A}}$. The volume of the unit cell in cm³ will be

• $1.6 \times {10}^{21} {\mathrm{cm}}^3$

• $2.81 \times {10}^{-23} {\mathrm{cm}}^3$

• $6.02 \times {10}^{-23} {\mathrm{cm}}^3$

• $6.6 \times {10}^{-24} {\mathrm{cm}}^3$

The density of solid argon is 1.65 g per cc at -233°C. If the argon atom is assumed to be a sphere of radius 1.54 × 10^-8 cm, what percent of solid argon is apparently empty space? (Ar = 40)

• 16.5%

• 38%

• 50%

• 62%

A solid compound XY has NaCl structure. If the radius of the cation is 100 pm, the radius of the anion (Y^- ) will be

• 275.1 pm

• 322.5 pm

• 241.5 pm

• 165.7 pm

Tetragonal crystal system has the following unit cell dimensions

• $\mathrm{a}=\mathrm{b}=\mathrm{c}, \mathrm{\alpha }=\mathrm{\beta }=\mathrm{\gamma }=90°$

• $\mathrm{a}=\mathrm{b}\ne \mathrm{c}, \mathrm{\alpha }=\mathrm{\beta }=\mathrm{\gamma }=90°$

• $\mathrm{a}\ne \mathrm{b}\ne \mathrm{c},\mathrm{\alpha }=\mathrm{\beta }=\mathrm{\gamma }=120°$

• $\mathrm{a}=\mathrm{b}\ne \mathrm{c},\mathrm{\alpha }=\mathrm{\beta }=90°, \mathrm{\gamma }=120°$

A crystalline solid

• changes rapidly from solid to liquid

• has no definite melting point

• undergoes deformation of its geometry easily

• soften easily

Frenkel defect is generally observed in

• AgBr

• Agl

• ZnS

• All of the above

Most crystals show good cleavage because their atoms, ions or molecules are

• weakly bonded together

• strongly bonded together

• spherically symmetrical

• arranged in planes