Phosphorus cannot form `PH_(5)` with its outer electronic configuration as `3s^(3)3p^(3)` because (A)phosphorus cannot show +5 oxidation state (B)P H 5 is not a stable compound (C)Δ a H value of dihydrogen and Δ e g H value of hydrogen do not favour higher oxidation state of phosphorus (D)phosphorus is not very reactive hence does not form P H 5

Options

A. phosphorus cannot show +5 oxidation state
B. `PH_(5)` is not a stable compound
C. `Delta_(a)H` value of dihydrogen and `Delta_(eg)H` value of hydrogen do not favour higher oxidation state of phosphorus
D. phosphorus is not very reactive hence does not form `PH_(5)`

Explanation

To determine why phosphorus cannot form \( PH_5 \) with its outer electronic configuration of \( 3s^2 3p^3 \), we need to analyze the options provided:

1. **Understanding the Electronic Configuration**:
- Phosphorus has an electronic configuration of \( 3s^2 3p^3 \). This means it has 5 valence electrons.
- The maximum oxidation state phosphorus can achieve is +5, which would require it to utilize all five of its valence electrons.

2. **Analyzing the Options**:
- **Option (A)**: "Phosphorus cannot show +5 oxidation state."
- This is incorrect because phosphorus can indeed show +5 oxidation state in compounds like \( PCl_5 \).

- **Option (B)**: "PH5 is not a stable compound."
- This option is partially true, but it doesn't directly explain why phosphorus cannot form \( PH_5 \).

- **Option (C)**: "ΔaH value of dihydrogen and ΔegH value of hydrogen do not favor higher oxidation state of phosphorus."
- This option is correct. The high enthalpy of atomization of hydrogen makes it difficult to form \( H \) atoms, and the low electron gain enthalpy of hydrogen means it cannot effectively oxidize phosphorus to the +5 state.

- **Option (D)**: "Phosphorus is not very reactive hence does not form PH5."
- While phosphorus is less reactive compared to some elements, this does not directly explain the inability to form \( PH_5 \).

3. **Conclusion**:
- The best explanation for why phosphorus cannot form \( PH_5 \) is given in option (C). The high enthalpy of atomization of hydrogen and the unfavorable electron gain enthalpy do not support the formation of phosphorus in the +5 oxidation state.

**Final Answer**: (C) ΔaH value of dihydrogen and ΔegH value of hydrogen do not favor higher oxidation state of phosphorus.

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