1. | X is an alkali metal and Y is an alkaline earth metal. |
2. | X is an alkaline earth metal and Y is an alkali metal. |
3. | Both X and Y are alkali metals. |
4. | Both X and Y are alkaline earth metals. |
For the second-period elements, the correct increasing order of first ionisation enthalpy is:
1. Li < Be < B < C < O < N < F < Ne
2. Li < Be < B < C < N < O < F < Ne
3. Li < B < Be < C < O < N < F < Ne
4. Li < B < Be < C < N < O < F < Ne