The lithium ion `(Li^(+))` and hydride ion `(H^(-))` are isoelectronic ions. Which statements about these system is true?

Options

A. Chemical properties of these ions are identical since they are isoelectronic.
B. `Li^(+)` is a stronger reducing agenet than `H^(-)`
C. More energy is needed to ionize `H^(-)` than `Li^(+)`
D. Radius of `H^(-)` is large than that of `Li`.

Answer

To determine which statements about the lithium ion (Li⁺) and hydride ion (H⁻) are true, we need to analyze the properties of these isoelectronic ions step by step.

### Step 1: Understand Isoelectronic Species
Isoelectronic species are atoms or ions that have the same number of electrons. Both Li⁺ and H⁻ have 2 electrons:
- Li⁺ has 3 protons and 2 electrons.
- H⁻ has 1 proton and 2 electrons.

### Step 2: Analyze Chemical Properties
The first statement claims that the chemical properties of these ions are identical since they are isoelectronic. This is **incorrect** because, despite having the same number of electrons, their chemical properties differ due to their different nuclear charges (number of protons).

### Step 3: Ionization Enthalpy Comparison
The second statement suggests that Li⁺ is a stronger reducing agent than H⁻. This is also **incorrect**. A reducing agent is one that donates electrons. H⁻ can easily lose an electron to become neutral hydrogen (H), while Li⁺ would require more energy to lose an electron to become Li²⁺. Therefore, H⁻ is a better reducing agent.

### Step 4: Ionization Energy
The third statement posits that more energy is needed to ionize H⁻ than Li⁺. This is **incorrect**. Ionizing H⁻ requires less energy compared to ionizing Li⁺ because Li⁺ has a higher effective nuclear charge due to having more protons, making it harder to remove an electron.

### Step 5: Compare Ionic Radii
The fourth statement claims that the radius of H⁻ is larger than that of Li⁺. This statement is **correct**. H⁻ has an additional electron compared to neutral hydrogen, which increases its size. In contrast, Li⁺, having lost an electron, has a smaller radius due to the increased effective nuclear charge acting on fewer electrons.

### Conclusion
Based on the analysis:
- Statement A: Incorrect
- Statement B: Incorrect
- Statement C: Incorrect
- Statement D: Correct

Thus, the correct statement is **D**: The radius of H⁻ is larger than that of Li⁺.

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