Statement I: The electron affinity of P is less than that of Si.
Statement II: Zef increases in a period from left to right. 

Options

A. If both Statement I and Statement II are true and Statement II is the correct explanation of Statement I.
B. If both Statement I and Statement II are true but Statement II is not the correct explanation for Statement I.
C. If Statement I is true but Statement II is false.
D. If Statement I is false but Statement II is true.

Answer

To solve the question, we need to analyze both statements provided and determine their validity.

### Step 1: Analyze Statement I
**Statement I:** The electron affinity of P is less than that of Si.

- **Understanding Electron Affinity:** Electron affinity refers to the amount of energy released when an electron is added to a neutral atom in the gas phase. Generally, electron affinity tends to increase across a period from left to right due to increasing nuclear charge.

- **Position in the Periodic Table:**
- Silicon (Si) is in Group 14.
- Phosphorus (P) is in Group 15.

- **Half-filled Configuration:** Phosphorus has a half-filled p subshell (3p³), which makes it relatively stable. This stability results in a lower tendency to gain an additional electron compared to silicon, which does not have a half-filled configuration.

- **Conclusion for Statement I:** Since phosphorus has a half-filled configuration, it is less likely to accept an electron compared to silicon. Therefore, the electron affinity of P is indeed less than that of Si. **Statement I is true.**

### Step 2: Analyze Statement II
**Statement II:** Z_eff increases in a period from left to right.

- **Understanding Z_eff:** Z_eff (effective nuclear charge) is the net positive charge experienced by an electron in a multi-electron atom. It accounts for the shielding effect of inner-shell electrons.

- **Trends in the Periodic Table:**
- As we move from left to right in a period, the number of protons in the nucleus increases, which increases the nuclear charge.
- Although additional electrons are added, they are added to the same energy level, leading to less effective shielding.

- **Conclusion for Statement II:** As a result, the effective nuclear charge (Z_eff) experienced by the outermost electrons increases across a period from left to right. **Statement II is true.**

### Step 3: Determine the Relationship Between the Statements
- Both statements are true, but they are independent of each other. The first statement discusses electron affinity, while the second discusses effective nuclear charge.

### Final Conclusion
Both statements are true, but they do not explain each other. Therefore, the correct option is that both statements are true but independent.

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