The highest electron affinity is shown by

The electronic configuration of two elements $\mathrm{X}$ and $\mathrm{Y}$ are given below:

$$\begin{gathered} \mathrm{X} = 1{\mathrm{s}}^2 2{\mathrm{s}}^2 2{\mathrm{p}}^6 3{\mathrm{s}}^2 3{\mathrm{p}}^6 4{\mathrm{s}}^2 ; \\ \mathrm{Y} = 1{\mathrm{s}}^2 2{\mathrm{s}}^2 2{\mathrm{p}}^6 3{\mathrm{s}}^2 3{\mathrm{p}}^5 \end{gathered}$$

The formula of the ionic compound that can be formed between these elements is