TG EAMCET 3 May 2025 Shift 2 Paper

The first ionisation enthalpy generally increases across a period due to increasing effective nuclear charge. However, exceptions to this trend occur when a stable electronic configuration is involved.
In the second period ( Li to Ne ), two such exceptions occur.
1. Beryllium (Be) The electronic configuration is 1s22s2. The first ionisation enthalpy of beryllium is higher than that of boron, the succeeding element. It is also higher than that of proceeding Ind element is lithium. This is due to the stable, completely filled 2 s subshell, which makes it more difficult to remove an electron.
2.Nitrogen ( N ) The electronic configuration is 1s22s22y3. The first ionisation enthalpy of nitrogen is higher than that of oxygen, the succeeding element. It is also higher than the proceeding element is carbon. This is because of the extra stability associated with the half-filled 2p subshell, which resists the removal of an electron.
Therefore, the two elements X and Y are beryllium ( Be ) and nitrogen ( N ).