What is the order of first,second,and third ionisation enthalpy? Why?

(N/A) The order of ionisation enthalpy is $3^{rd} > 2^{nd} > 1^{st}$.
This is because,as an electron is removed,the remaining electrons experience a greater effective nuclear charge due to the decrease in electron-electron repulsion and the constant nuclear charge.
Consequently,the attraction between the nucleus and the remaining electrons increases,requiring more energy to remove subsequent electrons.