Question

Among III-A group elements the elements with highest and lowest I.P. values are:

• A. B, Tl
• B. B, In
• C. B, Al
• D. B, Ga

Answer 1

The correct option is B B, In

$I.P.$ does not smoothly decrease down $III-A$ group. There is an observed discontinuity in the $I.P.$ values between $In$ and $Tl$ due to non availability of f-electrons, which have low screening effect to compensate the increase in nuclear charge.