A mineral having the formula AB₂ crystallizes in the cubic close-packed lattice , with the A atoms occupying the lattice points. The fraction of the tetrahedral sites occupied by B atoms is :

• 20 %

• 40 %

• 60 %

• 100 %

192.

A forms hcp lattice and B are occupying 1/3^rd of tetrahedral voids, then the formula of compound is

• AB

• A₃B₂

• A₂B₃

• AB₄

Which of the following is an amorphous solid?

• Iron

• Graphite

• Diamond

• Glass

The Ca²⁺ and F^- are located in CaF₂ crystal respectively at face-centred cubic lattice points and in

• tetrahedral voids

• half of tetrahedral voids

• octahedral voids

• half of octahedral voids

 Assertion: Monoclinic sulphur is an example of monoclinic crystal system.

 Reason: For a monoclinic system, a$\text{≠}$b $\text{≠}$ c and a$=$$\text{γ}$ = 90°, $\text{β}$$\text{≠}$90°.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

In bcc structure contribution of comer and central atom is

• $\frac{1}{8},1$

• $\frac{1}{4},\frac{1}{8}$

• $\frac{1}{8},\frac{1}{2}$

• $\text{1,}\frac{1}{2}$

Which defect causes decrease in the density of crystal ?

• Frenkel

• Schottky

• Interstitial

• F-centre

CsCl has bcc arrangement. Its unit cell edge length is 400 pm. Its inter-ionic distance is

• 400 pm

• 800 pm

• $\sqrt{3 }$$\times$100 pm

• $\frac{\sqrt{3}}{2}\times 400 \mathrm{pm}$

The crystal system of a compound with unit cell dimensions , a = 0.387 , b = 0.387 and c = 0.504 run and $\mathrm{\alpha }$ = $\mathrm{\beta }$ = 90° and $\mathrm{\gamma }$ = 120° is :

• cubic

• hexagonal

• orthorhombic

• rhombohedral

Tincture of iodine is :

• aqueous solution of I₂

• solution of I₂ in aqueous KI

• alcoholic solution of I₂

• aqueous solution of KI