JEE Main 2024 · 4 April · evening · Single correct · +4 / −1
Given below are two statements :
Statement I : The correct order of first ionization enthalpy values of Li, Na, F and Cl is Na<Li<Cl<F.
Statement II : The correct order of negative electron gain enthalpy values of Li, Na, F and Cl is Na<Li<F<Cl
In the light of the above statements, choose the correct answer from the options given below :
- (a) Statement I is true but Statement II is false
- (b) Both Statement I and Statement II are false
- (c) Statement I is false but Statement II is true
- (d) Both Statement I and Statement II are true
Answer and solution
Answer (d) Both Statement I and Statement II are true
Solution
Chemistry ma’am · 3 steps
Both orders hold. The only twist is that Cl, not F, has the most negative electron gain enthalpy.
- Ionisation enthalpy. Removing an electron gets harder going up a group and across a period. So Na is lowest, Li is a little higher, and the halogens are far higher, with small F above Cl.
- Electron gain enthalpy. Halogens gain an electron readily, while alkali metals barely do, so Na and Li are at the bottom. F is so small that its 2p shell is crowded. The added electron feels strong repulsion, so Cl releases more energy than F.
Element First IE (kJ mol⁻¹) Electron gain enthalpy (kJ mol⁻¹) Na 496 -53 Li 520 -60 Cl 1251 -349, most negative F 1681, highest -328 - So. Ionisation enthalpy follows Na<Li<Cl<F, and negative electron gain enthalpy follows Na<Li<F<Cl. Both statements are true, which is option (d).
The idea to keep. Ionisation enthalpy trends are clean: F beats Cl. Electron gain enthalpy has an exception: small F repels the incoming electron, so Cl has the most negative value of all.
Answer from the NTA final answer key. Solution by PrepWiser.