Identify the elements from the electronic configurations

We match each configuration in List I to its element:

• (a) $1s^2 2s^2$
  Total electrons $=4$ $\\Rightarrow$ Be
• (b) $1s^2 2s^2 2p^4$
  Total electrons $=8$ $\\Rightarrow$ O
• (c) $1s^2 2s^2 2p^3$
  Total electrons $=7$ $\\Rightarrow$ N
• (d) $1s^2 2s^2 2p^1$
  Total electrons $=5$ $\\Rightarrow$ B

Interpret $\Delta_i H$

Here $\Delta_i H$ denotes the first ionization enthalpy.

Recall approximate first ionization enthalpies

Standard values are approximately:

• Be $\approx 899\ \text{kJ mol}^{-1}$
• B $\approx 801\ \text{kJ mol}^{-1}$
• N $\approx 1402\ \text{kJ mol}^{-1}$
• O $\approx 1314\ \text{kJ mol}^{-1}$

These also agree with periodic trends:

• Be has higher IE than B because Be has a filled $2s^2$ subshell.
• N has higher IE than O because N has half-filled $2p^3$ stability.

Match List I with List II

• (a) Be $\to 899$ $\Rightarrow$ (ii)
• (b) O $\to 1314$ $\Rightarrow$ (iii)
• (c) N $\to 1402$ $\Rightarrow$ (iv)
• (d) B $\to 801$ $\Rightarrow$ (i)

So the correct matching is:

Compare with options

This corresponds to Option C.

Verification with stored answer

Stored correct answer = C.

Our derived answer also = C. Hence they agree.