Question

Which of the following is the correct order of the first ionisation energy?

• A. $Cu>Ag<Au$
• B. $Cu>Ag>Au$
• C. $N{a}^{+}>Ne>O>Na$
• D. $Ne>O>N{a}^{+}>N$

Answer 1

The correct option is C $N{a}^{+}>Ne>O>Na$

$N{a}^{+}-1s^{2}2s^{2}2p^{6}Ne-1s^{2}2s^{2}2p^{6}O-1s^{2}2s^{2}2p^{4}Na-1s^{2}2s^{2}2p^{6}3s^1$

Here, $N{a}^{+}$ and $Ne$ are having same electronic configuration but $N{a}^{+}$ has more number of protons than $Ne$ so the effective nuclear charge will be higher and therefore, the energy required to remove an electron from $N{a}^{+}$ is higher than $Ne$.
So, the correct order of the first ionisation energy will be
$N{a}^{+}>Ne>O>Na$