Question

Correct increasing order of $1st$ ionisation energy:

• A. $B<Be<C$
• B. $Be<B<C$
• C. $Be<C<B$
• D. None of the above

Answer 1

The correct option is A $B<Be<C$

Ionisation energy increses as we move from left to right in a period because effective nuclear charge increases and thus more energy will be required to remove an electron.
Accordingly one can expect the order of $1st$ ionisation energy as $Be<B<C$.

Be has higher first ionisation energy because of its fully- filled s orbital whereas B has only one electron in 2p- orbital. We know s-orbital has higher penetration power than p -orbital and in Be electron is removed from s- orbital and in B electron will be removed from p-orbital.
Therefore, correct increasing order of $1st$ ionisation energy is $B<Be<C$