Question

Which one of the following order is correct for the first ionisation energies of the elements?

• A. \(B<Be<N<O\)
• B. \(Be<B<N<O\)
• C. \(B<Be<O<N\)
• D. \(B<O<Be<N\)

Hint:

Remember: \(B < Be\) due to \(2p\) removal and \(O < N\) due to electron pairing repulsion in oxygen.

Answer 1

The Correct Option is C

Step 1: General trend.
Ionisation energy generally increases across a period due to increasing nuclear charge.
Step 2: Apply known exceptions.
- \(B\) has lower IE than \(Be\) because \(B\) loses a \(2p\) electron (easier to remove).
- \(O\) has lower IE than \(N\) because \(O\) has paired electrons in \(2p\) causing extra repulsion.
Step 3: Arrange with exceptions.
\[ B<Be<O<N \]
Final Answer:
\[ \boxed{B<Be<O<N} \]