Which pair of elements have chemical properties that are the most similar?

The same group species shared same amount of valence electron. This valence electron lead to find the chemical properties of species' .

The electronic configurations of Al and Ga is

Aluminum: $\left[\mathrm{Ne}\right]3{\mathrm{s}}^{2}3{\mathrm{p}}^1$

Gallium : $\text{ [Ar] }3{\mathrm{d}}^{10}4{\mathrm{s}}^{2}4{\mathrm{p}}^1$.

Their valence is +3. Hence, option B is correct.