The first ionization enthalpies of $\mathrm{Be}, \mathrm{B}, \mathrm{N}$ and O follow the order

(D) $\mathrm{B}<\mathrm{Be}<\mathrm{O}<\mathrm{N}$

(A) $\mathrm{O}<\mathrm{N}<\mathrm{B}<\mathrm{Be}$

(B) $\mathrm{Be}<\mathrm{B}<\mathrm{N}<\mathrm{O}$

(C) $\mathrm{B}<\mathrm{Be}<\mathrm{N}<\mathrm{O}$

JEE Main · 2022 · 25 Jul 2022 · Shift 2 · Classification of Elements and Periodicity

The first ionization enthalpies of

Be, B, N

and O follow the order

Answer: (D)

First ionization enthalpy depends on electronic configuration and stability:

N (

1 s^{2} 2 s^{2} 2 p^{3}

): Half-filled

2 p

subshell provides extra stability → highest IE

O (

1 s^{2} 2 s^{2} 2 p^{4}

): One electron paired in

2 p

→ slightly lower IE than N due to electron-electron repulsion

Be (

1 s^{2} 2 s^{2}

): Completely filled

2 s

subshell → relatively high IE

B (

1 s^{2} 2 s^{2} 2 p^{1}

): Single electron in

2 p

orbital, easier to remove → lowest IE

Order:

B < Be < O < N

JEE Main · 2022 · 25 Jul 2022 · Shift 2 · Single correct option