Q:

Ionisation energy is lower for higher energy shell?

Why does an electron in a higher energy orbital require less energy to remove it? Wouldn't it be harder to remove an electron from a higher energy orbital when compared to a lower energy orbital?

A:

It is difficult to remove an electron from lower energy shells because of very large electrostatic forces of attraction between the electrons and the positively charges nucleus.
As the distance between the nucleus and the electron increases with the number of shells, the electrostatic forces of attraction between the electrons of higher energy level and the nucleus decreases, and it becomes easier to remove an electron from that shell.
That is why it requires a large amount of energy to remove an electron from lower shell with respect to the electrons at higher shells.

