a)(i) Nuclear fission is a nuclear reaction in which a heavy nucleus is split into different lighter nuclei emitting neutrons with the release of a large amount of energy. (ii) Nuclear fusion is a nuclear reaction between two light nuclei at high temperatures formic a heavier nucleus with the release of a large amount of energy. (b)(i) Applications of atomic energy are: - for the production of nuclear weapons for warfare - in the generation of electric power - for health diagnosis and radiotherapy - to detect leakages. In underground pipes carrying oils or gases. (ii) Half life is the time required for radioactive substance to decay to half of its original quantity. (iii) T = \(\frac{0.693}{\lambda}\) (c)(i) \(^{226}_{88} X \) ---> \(^{222}_{88} Y + ^4_2He\) By the emission of \(\alpha\) the mass number of X decreases by 4 the atomic number by 2 to give daughter nucleus Y (ii) \(^{222}_{86} Y \) ---> \(^{222}_{87} Z + ^0_{-1} e\) By the emission of \(\beta\) particle the mass number of Y is unchanged while the atomic number of Y is unchanged while the atomic number is increased by 1. (iii) \(^{226}_{87} Z \) ---> \(^{222}_{87} Z + ^0_0\gamma\) By emission of \(\gamma\) radiation, the mass and atomic number of Z remain unchanged.