491.

The incorrect statement among the following is

• C₆₀ is an allotropic form of carbon

• O_3, is an allotropic form of oxygen

• S₈ is only allotropic form of sulphur

• red phosphorus is more stable in air than white phosphorus.

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

If Z is the number of atoms in the unit cell that represents the closest packing sequence... A B C A B C..., the number of tetrahedral voids in the unit cell is equal to

• Z

• 2Z

• Z/2

• Z/4

What is the co-ordination number of Cl^- in NaCl crystal ?

• 8

• 6

• 4

• 3

Assertion : Graphite is an example of tetragonal crystal system.

Reason : For a tetragonal system, a = b $\ne$ c, $\mathrm{\alpha }$=$\mathrm{\beta }$= 90°,$\mathrm{\gamma }$= 120°

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

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

• If assertion is true, but reason is false.

• Both assertion and reason are false statements.

Schottky defect defines imperfection in the lattice structure of a :

• solid

• gas

• liquid

• plasma

An AB₂ type structure is found in :

• NaCl

• CaF₂

• Al₂O₃

• N₂O

An element (atomic mass 100 g/mol) having BCC structure has unit cell edge 400 pm. The density of element is (No. of atom in BCC (Z) = 2).

• 2.144 g/cm³

• 7.289 g/cm³

• 5.188 g/cm³

• 10.376 g/cm³

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

• Cubic

• Hexagonal

• Orthorhombic

• Rhombohedral

A solid AB has NaCl type structure. The radius of A⁺is 100 pm. What is the radius of B^-?

• 190.47

• 540.13

• 525

• 78.12