The source of energy of the sun and stars is obtained from the nuclear fusion of :

1. uranium
2. thorium
3. hydrogen
4. ²³⁵₉₂U

The temperature required for the process of nuclear fusion is nearly:

1. 1000 K
2. 10⁴ K
3. 10⁵ K
4. 10⁷ K

Complete the following fusion reactions —

(a) ${}_2^3\text{He}${2}^{3}\text{He} + ${1}^{2}\text{H}$ ⟶ ${}_2\text{He}${2}\text{He} + ${1} \text{H}$ + energy

(b) ${}_1^2\text{H}${1}^{2}\text{H} + ${1}^{2}\text{H}$ ⟶ $_{2}\text{He}$ + $^{1} \text{n}$ + energy

(a) Name the process, nuclear fission or nuclear fusion, in which the energy released per unit mass is more?

(b) Name the process, fission or fusion which is possible at ordinary temperature.