Both `PH_(3)` and `PH_(5)` exist .

Explanation

To determine whether both PH₃ (phosphine) and PH₅ (phosphorus pentahydride) exist, we can analyze the bonding and electronic configuration of phosphorus.

### Step-by-Step Solution:

1. **Understanding Covalency**:
- Covalency refers to the number of bonds an atom can form. For phosphorus in PH₃, the covalency is 3, meaning it forms three bonds with hydrogen atoms.

2. **Electronic Configuration of Phosphorus**:
- The electronic configuration of phosphorus is:
\[ \text{Neon} \, 3s^2 \, 3p^3 \]
- This indicates that phosphorus has 5 valence electrons (2 in the 3s subshell and 3 in the 3p subshell).

3. **Ground State Configuration**:
- In its ground state, phosphorus has three unpaired electrons in the 3p subshell. These unpaired electrons can form bonds with hydrogen, resulting in PH₃.

4. **Excited State Configuration**:
- In the first excited state, one of the 3s electrons can be promoted to the 3d subshell, allowing phosphorus to have five unpaired electrons:
\[ \text{3s}^1 \, \text{3p}^3 \, \text{3d}^1 \]
- This configuration allows phosphorus to form five bonds, leading to the formation of PH₅.

5. **Presence of Vacant d-Orbitals**:
- The presence of vacant 3d orbitals enables phosphorus to expand its covalency from 3 to 5. This is why both PH₃ and PH₅ can exist.

6. **Conclusion**:
- Therefore, both PH₃ and PH₅ exist in nature, making the statement true.

### Final Answer:
The statement is true; both PH₃ and PH₅ exist.

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