Question

The first $({\left(\Delta \right)}_i{H}_1)$ and second $({\left(\Delta \right)}_i{H}_2)$ ionization enthalpies (in kJ $mo{l}^{-1}$ ) and the electron gain enthalpy $({\left(\Delta \right)}_{eg}H)$ (in kJ $mo{l}^{-1}$ ) of the elements I, II, III, IV and V are given below:

Element	${\Delta }_i{H}_1$	${\Delta }_i{H}_2$	${\Delta }_{eg}H$
I	$520$	$7300$	$-60$
II	$419$	$3051$	$-48$
III	$1681$	$3374$	$-328$
IV	$1008$	$1846$	$-295$
V	$2372$	$5251$	$+48$

The most reactive metal and the least reactive non-metal of these are respectively

• A. V and II
• B. II and V
• C. V and III
• D. IV and V

Answer 1

Answer: (B)

$\Delta H_1=520$
$\Delta H_2=7300$
$\Delta H_2$ is $10$ times greater than $\Delta H_1$ mean first $e^{-}$ remove from inner shell {Ionisation energy decreases the number of shells increases because $Z_{eff}$ decreases hence, removal of electron is easy so, $I.E.\downarrow$
III ${\Delta }_i{H}_1<{\Delta }_i{H}_2$
IV ${\Delta }_i{H}_1<{\Delta }_i{H}_2$
V ${\Delta }_i{H}_1<{\Delta }_i{H}_2$
$\Delta H_{eff}H=+ve$
$\Delta H_{eff}H=+ve$ Means it belongs to inert gas & these are belongs to non-metal and very less reactive
So, II most reactive metal.
V is least reactive non-metal.