I₁ of an element X is 899 kJ mole^–1 and that of another element Y is 801 kJ mole^–1. Then X and Y may be

Since, 899 $\mathrm{kJ}{ \mathrm{mole}}^{-1}\left(\mathrm{X}\right) \mathrm{comesbefore} 801\text{ kJ mole }{}^{-1}(\mathrm{Y})$.

The first element will have higher ionization energy over second element. 

Only Optioin B satisfies this condition. Therefore, Option B is the correct answer.