Which one among the following statements is/are not correct?
I. Ba compounds, generally are more covalent than Be compounds.
II. The electron gain enthalpy of He is positive.
The oxidation state of O in `OF_(2)andNa_(2)O` are same.
IV. The radius of `Na^(+)` ion is smallare than that of `F^(-)` ion.

Options

A. I, III, IV
B. II
C. II, III, IV
D. I, II

Answer

D

Explanation

The explanation of given statements are :
I. Both beryllium (Be) and barium (Ba) belongs to the same group (i.e. group-II) and as we move down the group , size of atom/ion increases while their covalent character decreases. Thus, Ba compounds are generally less covalent than Be compounds .
(II) .The electron gain enthalpy of He is positive because of very small size with full-filled electronic configuration .(i.e. `Is^(2)`) . Hence, the given statement is correct .
III. The oxidation state of O in ` OF_(2) = + I ` and oxidation state of O in ` Na_(2)O = - 1` IIence, the given statement is not correct .
IV. The radius of `Na^(+)` ion is smaller then ` F^(-)` ion because both are isoelectronic species but ` F^(-)` has less number of protons (i.e. more number of electrons) [i.e. F has 9 protons ] , than that of ` Na^(+)` ( has 11 protons ).
Hence , ` Na^(+)` ion is of smaller in size then that of ` F^(-)` ion (due to greater attractive force in sodium.)
Thus , I and III are not the correct statements .
Hence, option (d) is the correct answer .