The first ( Δ i H 1 ) and second ( Δ i H 2 ) ionization enthalpies (in kJ m o l - 1 ) and the electron gain enthalpy ( Δ e g H ) (in kJ m o l - 1 ) of the elements I, II, III, IV and V are given below: Element Δ i H 1 Δ i H 2 Δ e g 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

Step-by-step solution

∆ H 1 = 520 ∆ H 2 = 7300 ∆ H 2 is 10 times greater than ∆ H 1 mean first e - remove from inner shell Ionisation energy decreases the number of shells increases because Z e f f decreases hence, removal of electron is easy so, I . E . ↓ III ∆ i H 1 < ∆ i H 2 IV ∆ i H 1 < ∆ i H 2 V ∆ i H 1 < ∆ i H 2 ∆ H e f f H = + v e ∆ H e f f H = + v e 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.