Define ionsiation enthalpy. State its units. 

What are successive ionisation enthalpies? Explain why the second ionisation enthalpy is higher than the first ionisation enthalpy?

Discuss in brief the factors which influence the magnitude of ionsiation enthalpy.

How does ionisation enthalpy vary along a group?

What are the various factors due to which the ionization enthalpy of the main group elements tends to decrease down a group?

Why does the first ionsiation enthalpy increase as we go from left to right through a period of the periodic table?
Or
How does ionisation enthalpy vary along a period? 

Why is ionisation enthalpy of Be more than that of B?

Why ionsiation enthalpy of N is more than that of O even though oxygen has higher nuclear charge than nitrogen?

Ionsiation enthalpy of fluorine is greater than that of oxygen. Explain.

Why do noble gases have very high value of ionisation enthalpy?