• question_answer 41) The first $({{\Delta }_{i}}{{H}_{1}})$ and the second $({{\Delta }_{i}}{{H}_{2}})$ionisation enthalpies$(in\,kJ\,mo{{l}^{-1}})$ and the $({{\Delta }_{eg}}H)$ electron gain enthalpy of a few elements are given below: Elements ${{\Delta }_{\mathbf{i}}}{{\mathbf{H}}_{\mathbf{1}}}$ ${{\Delta }_{\mathbf{i}}}{{\mathbf{H}}_{\mathbf{2}}}$ ${{\Delta }_{eg}}\mathbf{H}$ 1. 520 7300 60 2. 419 3051 48 3. 1681 3374 328 4. 1008 1846 295 5. 2372 5251 + 48 6. 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 conform a stable binary halide of the formula $M{{X}_{2}}$ (X = halogen). (f) the metal which can form a predominantly stable covalent halide of the formula MX (X = halogen).

(a) The element 5 has highest first ionisation enthalpy and positive electron gain enthalpy is the member of inert gases. It is least reactive. (b) The element 2 has the least first ionization enthalpy and low electron gain enthalpy is highly electropositive and hence, most reactive metal. (c) The element 3 has high first ionisation enthalpy and highest electron gain enthalpy is highly electronegative and hence most reactive non-metal (probably halogen). (d) The element 4 has comparatively high ionisation enthalpy and high electron gain enthalpy. It seems to be a higher member of halogen group (probably iodine) which is least reactive non-metal. (e) The element 6 has comparatively low first ionisation enthalpy and low electron gain enthalpy. It is an alkaline earth metal. It forms halide, $M{{X}_{2}}$. (f) The element first has low first ionisation enthalpy and a very high second ionisation enthalpy seems to be an alkali metal. It forms halide, MX.