# The Solid State

Question 49

## Why does zinc oxide exhibit enhanced electrical conductivity on heating?

Solution
Zinc oxide is white in colour at room temperature. On heating it loses oxygen and turns yellow.On heating, zinc oxide loses oxygen

The excess zinc ions are accomodated in interstitial sites with electrons trapped in the neighbourhood. The enhanced conductivity is due to these trapped electrons.
Question 50

## In a body centred unit cell, one of the diagonals contains two extra atoms. Find the number of atoms present per unit cell?

Solution

In a body centred unit cell diagonal contain two extra atom .so in per unit cell  = $8×\frac{1}{8}+2=3.$

Question 51

## An element occurs in the bcc structure. How many atoms are present in its unit cell explain ?

Solution
body centre wholly belongs to the unit cell in which it is present. Thus in a body-centered cubic (bcc) unit cell:
(i) 8 corners × 1/8 per corner atom $8×1/8$ = 1 atom
(ii) 1 body centre atom = 1 × 1 = 1 atom
∴ Total number of atoms per unit cell = 2 atoms.
Question 52

## What is the number of atoms per unit cell in a body centred cubic structure?

Solution
The number of atoms per unit cell in a body centred cubic structure = 2.