Question

Which pair represents incorrect first IE?

• A. $Be>B$
• B. $N>O$
• C. $Li>Na$
• D. $He>H{e}^{+}$

Answer 1

Answer: (D)

The pair $He>H{e}^{+}$represents incorrect first IE.
The pair $He<H{e}^{+}$represents correct first IE.
The pair $He,H{e}^{+}$corresponds to first and second ionisation energies of $He$.
It is difficult to remove an electron from cation than from neutral atom. Hence, second ionisation energy of $He$ is higher than first ionisation energy of $He$.
$I{E}_2>I{E}_1$