The first ionisation potential of Na, Mg, Al and Si are in the order

Options

A. `Na lt Mg gt Al lt Si`
B. `Na gt Mg gt Al gt Si`
C. `Na lt Mg lt Al gt Si`
D. `Na gt Mg gt Al lt Si`

Answer

A

Explanation

`IE_1` of Mg is higher than that of Na because of increased nuclear charge and also than that of Al because in Mg an s-electron has to be removed. While in Alit is 3p electron that has to be removed. Mg also has stable fully filled configuration. The `IE_1` of Si is, however, higher than those of Mg and Albecause of increased nuclear charge. Thus, the overall order is Na < Mg > A < Si.