Question

why boron has lower ionisation enthelpy than barelium​

Answer 1

Boron-

${1s}^{2} \: {2s}^{2} \: {2p}^{1}$

Berylium

${1s}^{2} \: {2s}^{2}$

Since boron half fully filled orbital and its not so in berylium, boron has lower ionisation enthelpy than barelium