Question

The first ($\Delta H_1$) and second ($\Delta H_2$) ionisation enthalpies (in $kJmo{l}^{-1}$) and the electron gain enthalpy (${\Delta }_{eg}H$) (in $kJmo{l}^{-1}$) of the elements I, II, III, IV and V are given below:

Element	${\Delta }_1{H}_1$	${\Delta }_1{H}_2$	${\Delta }_{eg}H$
I	520	7300	-60
II	419	3051	-48
II	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. I and V
• B. V and II
• C. II and V
• D. IV and V

Answer 1

The correct option is C II and V

I represents $Li$, II represents $K$, III represents $Br$, IV represents $I$, V represents $He$. So, amongst these, II represents most reactive metal and V represents least reactive non-metal.

Also, II has the lowest value of first ionization enthalpy and V has positive electron gain enthalpy.