Match the correct ionisation enthalpies and electron gain enthalpies of the following elements.

(i)Most reactive non metalA4193051– 48
(ii)Most reactive metalB16813374– 328
(iii)Least reactive elementC7381451– 40
(iv)Metal forming binary halideD2372525148

(1) (i) – B, (ii) – A, (iii) – D, (iv) – C
(2) (i) – A, (ii) – B, (iii) – D, (iv) – C
(3) (i) – C, (ii) – D, (iii) – B, (iv) – A
(4) (i) – B, (ii) – C, (iii) – A, (iv) – D

Answer: Option 1
Here, △H1 is first ionisation enthalpy and
△H2 is second ionisation enthalpy
and △egH is electron gain enthalpy

(i) Most reactive non-metal has high △H1 and high △H2 and most negative △egH. Therefore , the element is B.
(ii) Most reactive metal has low △H1 and higher △H2 (because the second electron has to be lost from the noble gas configuration) and has small negative △egH. Therefore, the element is A
(iii) Noble gases are the least reactive elements. They have very higher △H1 and △H2 and have positive △egH values. Thus the element is D.
(iv) Metal forming binary halides are halides are alkaline earth metals. They have △H1 and △H2 values little higher than those of most reactive metals (such as A) and have comparatively slightly less negative △egH values. Thus the element is C.

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