Ammonia molecule is a nucleophile in nature as it has unpaired electrons. This nucleophile attacks the chloromethane molecule and form methyl amine or methanamine by nucleophilic substitution reaction. The carbon atom is partially positive in the molecule, due to electronegativity of the halide attached which is partially negative. The electron-rich nucleophile attacks the positive ion, causing the halide ion to be separated from the molecule. The correct answer is (iii).