Assertion (A) 16 th group elements have higher ionisation enthalpy values than 15 th group elements in the corresponding periods.

Reason (R) 15 th group elements have half-filled stable electronic configurations.

Assertion (A) Fluorine has smaller negative electron gain enthalpy than chlorine.

Reason (R) The electron-electron repulsion is higher in chlorine than in fluorine.

In which of the following, elements are arranged in the correct order of their electron gain enthalpies?

In second period of the long form of the periodic table an element $$X$$ has second lowest first ionisation enthalpy and element $$Y$$ has second highest first ionisation enthalpy values. What are $$X$$ and $$Y$$ ?