JEE Main 2023 — Classification of Elements and Periodicity in Properties Question with Solution

A is incorrect. $\mathrm{F}$ and $\mathrm{Cl}$ belong to the same group of the periodic table. The electron gain enthalpy usually becomes less negative on moving down a group. However, in this case, the value of the electron gain enthalpy of $\mathrm{Cl}$ is more negative than that of $\mathrm{F}$. This is because the atomic size of $\mathrm{F}$ is smaller than that of $\mathrm{Cl}$. 

B is correct (ionisation energy decreases down the group).

C is incorrect (Electronegativity is a fixed property of an element and is typically measured on scales such as the Pauling scale or the Mulliken scale.). 

D is incorrect. The oxides which behave as both acidic and basic oxides are called amphoteric oxides. . Here ${\mathrm{Al}}_2{\mathrm{O}}_3$ is amphoteric oxide and $\mathrm{NO}$ is neutral oxide.

Hence, A, C and D are incorrect.