An alkyl halide with β-hydrogen atoms when reacting with a base or a nucleophile can undergo a particular type of reaction depending on the nature of the alkyl halide, the strength of the base or nucleophile, the size of the molecules and the conditions of the reaction. An alkyl halide can follow substitution or elimination reaction, and can also follow the two types of substitution, S_N1 or S_N2. A primary alkyl halide will prefer a S_N2 reaction as the incoming nucleophile cannot interact with the bulky substituents on or near the carbon atom thus having an inhibiting effect. Hence, primary alkyl halides and methyl halides have the highest tendency towards an S_N2 reaction. The correct answer is (ii).