Among the statements from I to IV, choose the correct option.
(I) Be has smaller atomic radius compared to Mg
(II) Be has higher ionization enthalpy than Al.
(Ill) Charge/radius ratio of Be is greater than that of Al.
(IV) Both Be and Al form mainly covalent compounds.

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(I), (II) and (Ill)

(II), (III) and (IV)

(I), (ll) and (IV)

(I), (Ill) and (IV)

answer is D.

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Detailed Solution

Both Be and Mg belongs to the same group, but Be belongs to the second period and Mg belongs to the third group. Atomic size of elements increases on moving down the group because of an addition of extra shell. Therefore, the atomic size of Mg is greater than the atomic size of Be.
Be belongs to the second group and Al belongs to the third group. Because of the small size and high effective nuclear charge, ionization energy is more in Be than Al.
Charge on Be is +2 and charge on Al is +3. Although atomic size is more for Al, but the change in atomic size is calculated in Angstroms which is smaller unit compared to charge. So, the charge/radius ratio comparison for Be and Al is done on the basis of charge. As charge is more in Al than Be, therefore the charge/radius is more in Al than Be.
Be and Al has high polarization power due to high value of charge/radius. Therefore, both predominantly form covalent compounds.

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