Which one out of O and Se is bigger in size and why?

Which one out of Na⁺ and Cl^- is bigger in size and why?

Out of P^3-,  S^2- and Cl^- ions, which has the smallest value of ionic radius and why?

Out of the following which has the smallest ionic 'Size and why: Li⁺, Na⁺, K⁺?

What is the trend of ionisation enthalpy in a period?

What is the trend of ionisation enthalpy in a group?

Among the elements Li, K, Ca, S and Kr, which one has the highest first ionisation enthalpy and which one has the lowest first ionisation enthalpy?

For each of the following pairs state which one has greater ionisation enthalpy:
(i) I, I^- (ii) Br, K.

From amongst the following, choose the element with the lowest IE: Be, B and C.

What is the relationship between the first ionisation enthaplies and metallic properties?