Interpret Statement I

Statement I gives the order of first ionization enthalpy for $\mathrm{Li}, \mathrm{Na}, \mathrm{F}, \mathrm{Cl}$ as: $\mathrm{Na} < \mathrm{Li} < \mathrm{Cl} < \mathrm{F}$

Check periodic trend of first ionization enthalpy

• Ionization enthalpy decreases down a group: $\mathrm{Li} > \mathrm{Na}, \quad \mathrm{F} > \mathrm{Cl}$
• Ionization enthalpy generally increases across a period from left to right: $\mathrm{Li} < \mathrm{F}, \quad \mathrm{Na} < \mathrm{Cl}$

Combining these: $\mathrm{Na} < \mathrm{Li} < \mathrm{Cl} < \mathrm{F}$

So, Statement I is true.

Interpret Statement II

Statement II gives the order of negative electron gain enthalpy for $\mathrm{Li}, \mathrm{Na}, \mathrm{F}, \mathrm{Cl}$ as: $\mathrm{Na} < \mathrm{Li} < \mathrm{F} < \mathrm{Cl}$

Check periodic trend of negative electron gain enthalpy

Here “negative electron gain enthalpy” means we compare the magnitude of electron gain enthalpy on the negative scale.

Relevant facts:

• Among alkali metals: $\mathrm{Na} < \mathrm{Li}$ because electron gain enthalpy becomes more negative from $\mathrm{Na}$ to $\mathrm{Li}$.
• Between halogens: $\mathrm{Cl} > \mathrm{F}$ on the negative electron gain enthalpy scale, because actual electron gain enthalpy of $\mathrm{Cl}$ is more negative than that of $\mathrm{F}$.
• Halogens have much more negative electron gain enthalpy than alkali metals.

Therefore the correct order is: $\mathrm{Na} < \mathrm{Li} < \mathrm{F} < \mathrm{Cl}$

So, Statement II is true.

Evaluate options

• A: Statement I true, Statement II false ✗
• B: Both false ✗
• C: Statement I false, Statement II true ✗
• D: Both true ✓

Final answer

$\boxed{\text{D}}$

Comparison with stored answer

Stored correct answer: D

My derived answer: D

Hence, they agree.