Question

Which of the following is not the correct increasing order of ionization energy?

• A. $C{l}^{-}<Ar<K^{+}$
• B. Au < Ag < Cu
• C. Cs < Rb < K
• D. K < Ca < Sc

Answer 1

The correct option is B

Au < Ag < Cu

Let's look at each of the options.

$C{l}^{-}<Ar<K^{+}$
These are isoelectronic species. But look at the number of protons. It is increasing in the given order. So, I.E. also increases.

Au < Ag < Cu
Ionization potential decreases down a group. This is incorrect.

Cs < Rb < K
Ionization potential decreases down a group. This is correct.

K < Ca < Sc
Ionization potential increases across a period. This is correct.