In second period of the modern periodic table, two elements $X$ and $Y$ have higher first ionisation enthalpy values than the preceding and succeeding elements. $X$ and $Y$ are respectively

$$ \text { Match the following. } $$

The correct answer is

Observe the following data ( $\Delta_t H_1, \Delta_t H_2$ and $\Delta_{\mathrm{eg}} H$ represent the first, second ionisation enthalpies and electron gain enthalpy respectively)

Using the data identify the most reactive metal.

Atomic numbers of three elements $E_1, E_2$ and $E_3$ of periodic table are $Z_1, 50$ and $Z_2$ respectively. From the position of the elements shown in figure, the values of $\left(Z_2-Z_1\right)$ is