In a period, the first ionisation enthalpy of the element at extreme left and the negative electron gain enthalpy of the extreme right element, except noble gases, are respectively.
- (A)lowest and lowest
- (B)highest and lowest
- (C)lowest and highest✓ Correct
- (D)highest and highest
Answer: (C)
Solution
The element at the extreme left of a period is a group 1 metal, which holds its valence electron most loosely and so has the lowest first ionisation enthalpy of the period. The element at the extreme right apart from the noble gas is a group 17 halogen, which is one electron short of a closed shell and releases the most energy on gaining an electron, giving the highest magnitude of negative electron gain enthalpy. The two quantities are respectively lowest and highest.
JEE Main · 2026 · 06 Apr 2026 · Shift 2 · Single correct option