Of the elements given. which has the lowest ionization energy?

Examine the available choices. The largest atomic radius among the other three atoms is that of Sulphur.

 Sulphur's electrical arrangement is also $\left[\mathrm{Ne}\right]3{\mathrm{s}}^{2}3{\mathrm{p}}^4$. Sulfur can reach the half-filled state and hence acquire improved stability by shedding one electron. As a result, in this situation, Sulphur has the lowest ionization enthalpy.