The first `(Delta_(i)H_(1))` and second `(Delta_(i)H_(2))` ionisation enthalpies `("in" kJ mol^(-1))` and the `(Delta_(eg)H^(ө))` electron gain enthalpy `("in" kJ mol^(-1))` of a few elements are given below:
`{:("Elements",(Delta_(i)H_(1)),(Delta_(i)H_(2)),Delta_(eg)H^(ө)),(I,520,7300,-60),(II,419,3051,-48),(III,1681,3374,-328),(IV,1008,1846,-295),(V,2372,5251,+48),(VI,738,1451,-40):}`
Which of the above elements is likely to be
a. the least reactive element.
b. the most reactive metal.
c. the most reactive non-metal.
d. the least reactive non-metal.
e. the metal which can form a stable binary halide of the formula MX (X=halogen).
f. the metal which can form a predominantly stable covalent halide of the formula MX(X=halogen).

Explanation

a. The element `V` which has the highest `IE_(1)` and positive. `(Delta_(eq)H^(ө))` is the least reactive elements. Since inert gases have positive `(Delta_(eq)H^(ө))` , therefore, the element `V` must be an inert gas. The values of `IE_(1)`,`IE_(2)` and `(Delta_(eq)H^(ө))` match that of helium `(He)`.
b. The element `II` which has the least `IE_(1)` and a low negaive `(Delta_(eq)H^(ө))` is the recative metal. The values of `IE_(1)`,`IE_(2)` and `(Delta_(eq)H^(ө))` match that of `K` (potassium).
c. The element `III` which has high ` IE_(1)` and a very high negative `(Delta_(eq)H^(ө))` is the recative non-metal. The values of `IE_(1)`,`IE_(2)` and `(Delta_(eq)H)` match that of `F` (fluorine).
d. The element `IV` has a high negative `(Delta_(eq)H^(ө))` but not so high ` IE_(1)` . Therefore, it is the least reactive non-metal. The values of `IE_(1)`,`IE_(2)` and `(Delta_(eq)H^(ө))` match that of `I` (Iodine).
e. The element `VI` has low ` IE_(1)` but higher than that of alkali metals. Therefore, it appears that the element is an alkaline earth metal and hence will form binary halide of the formula `MX_(2)`(where `X`=halogen). The values of `IE_(1)`,`IE_(2)` and `(Delta_(eq)H^(ө))` match that of `Mg` (magnesium).
f. The element `I` has low `IE_(1)` but a very high `IE_(2)`, therefore, it must be an alkali metal. Since the metal forms a predominantly stable covalent halide of the formula MX(X=halogen), therefore ,the alkali metal must be least reactive. The values of `IE_(1)`,`IE_(2)` and `(Delta_(eq)H^(ө))` match that of `Li` (llithium).