Question

As u go down a group the ionisation energy increases or decreases

Answer 1

Ionization energy is the energy required to remove an electron or electrons from a neutral atom to form a cation.
Ionization energy decreases on going down a group.
On going down the group, an extra shell is added and electron to be removed is placed farther from the nucleus. The number of electrons between the valence shell and the nucleus increases and these intervening electrons shield the outer valence electrons from the attractive forces of the nucleus. This decreases the attractive forces between the nucleus and the electrons and hence less energy is required to remove the electron.