Question

Which of the following alkali metals have the least ionization enthalpy?

• A. $Li$
• B. $Na$
• C. $K$
• D. $Cs$

Answer 1

The correct option is D $Cs$

I.E. of the alkali metals are considerably low and decrease down the group from Li to Cs.
The effect of increasing size outweighs the increasing nuclear charge and the outermost electron is very well screened from the nucleus.