The order of decreasing ionisation ethalpy in alkali metals is

Options

A. `Na gt Li gt K gt Rb`
B. `Rb lt Na lt K lt Li`
C. `Li gt Na gt K gt Rb`
D. `K lt Li lt Na lt Rb`

Answer

C

Explanation

Ionisation enthalpy of alkali metals decreases down the group from Li to Cs. This is because of increase in size which outweighs the increasing nuclear charge, and the outermost electron is very well screened from the nuclear charge.