Question

The first $({\Delta }_i{H}_1)$ and the second $({\Delta }_i{H}_2)$ ionization enthalpies (in $kjmo{l}^{-1})$ and the $({\Delta }_{eg}H)$ electron gain enthalpy (in $kjmo{l}^{-1})$ of a few elements are given below:

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

Which of the following is least reactive element?

• A. Element I
• B. Element V
• C. Element IV
• D. Element II

Answer 1

Answer: (B)

The element V has highest first ionisation enthalpy and positive electron gain enthalpy. Hence it is least reactive and is a member of inert gases.