PCl₅ molecule has

(1) three fold axis of symmetry

(2) two fold axis of symmetry

(3) both

(4) none of these

Which of the following statements is correct about the conduction of electricity in pure crystal of silicon atroom temperature?

(1) The conduction is due to electrons present in fully occupied lowest energy states.

(2) The conduction is due to only some electrons capable of leaving the bonds at room temperature.

(3) The conduction is only due to the holes formed from the release of electrons.

(4) The conduction is due to the movement of both the electrons released and holes formed.

Calculate the Miller indices of crystal planes which cut through the crystal axes at (i) (2a, 3b, c), (ii) (∞, 2b, c )

(1) 3, 2, 6 and 0, 1, 2

(2) 4, 2, 6 and 0, 2, 1

(3) 6, 2, 3 and 0, 0, 1

(4) 7, 2, 3 and 1, 1, 1

Caculate the distance between 111 planes in a crystal of Ca. Repeat the calculation for the 222 planes. (a = 0.556nm)

(1) 016.1 nm

(2) 0.161 nm

(3) 0.610 nm

(4) None of the above

A metallic element crystallizes into a lattice containing a sequence of layers of ABABAB ............ Any packing of spheres leaves out voids in the lattice. The percentage by volume of empty space of this is

(1) 26%

(2) 21%

(3) 18%

(4) 16 %

Silver metal crystallises in a cubic closest – packed arrangement with the edge of the unit cell having a length a = 407 pm. What is the radius of silver atom.

(1) 143.9 pm

(2) 15.6 pm

(3) 11.59 pm

(4) 13.61 pm

From the fact that the length of the side of a unit cell of lithium is 351 pm. Calculate its

atomic radius. Lithium forms body-centered cubic crystals.

(1) 152.69 pm

(2) 62.71 pm

(3) 151.98 pm

(4) 54.61 pm

Atomic radius of silver is 144.5 pm. The unit cell of silver is a face centred cube. Calculate the density of silver.

(1) 10.50 g/cm³

(2) 16.50 g/cm³

(3) 12.30 g/cm³

(4) 15.50 g/cm³

A metallic element exists as a cubic lattice. Each edge of the unit cell is 2.88 Å. The density of the metal is 7.20 g cm^–3.  The number of unit cells, that will be present in 100 gm of the metal is: 

1. 5.82 × 10²³

2. 16.33 × 10²³

3. 7.49 × 10²⁴

4. 6.9 × 10²⁴

Silver crystallizes in a face centred cubic system, 0.408 nm along each edge. The density of silver is 10.6 $g/c{m}^3$ and the atomic mass is 107.9 g/mol. Calculate Avogadro's number.

(1) $6.00\times {10}^{23}$ atom/mol

(2) $9.31\times {10}^{23}$ atom/mol

(3) $6.23\times {10}^{23}$ atom/mol

(4) $9.61\times {10}^{23}$atom/mol