Which of the following species has equal number of `sigma- and pi-` bonds?

Options

A. `(CN)_(2)`
B. `CH_(2)(CN)_(2)`
C. `HCO_(3)^(-)`
D. `XeO_(4)`

Explanation

To determine which of the given species has an equal number of sigma (σ) and pi (π) bonds, we need to analyze the bonding in each species. Let's go through the options step by step.

### Step 1: Understand the Bonding Types
- **Single Bond**: 1 σ bond, 0 π bonds
- **Double Bond**: 1 σ bond, 1 π bond
- **Triple Bond**: 1 σ bond, 2 π bonds

### Step 2: Analyze Each Option

#### Option 1: C₂N₂
- Structure: C≡N - C≡N
- Bonds:
- Each C≡N has 1 σ bond and 2 π bonds.
- Total for 2 C≡N:
- σ bonds = 1 + 1 = 2
- π bonds = 2 + 2 = 4
- Conclusion: 2 σ bonds and 4 π bonds (not equal).

#### Option 2: CH₂CN₂
- Structure: H₂C - C≡N - C≡N
- Bonds:
- H₂C has 1 σ bond (C-H) and 1 σ bond (C-C).
- Each C≡N has 1 σ bond and 2 π bonds.
- Total:
- σ bonds = 1 (C-H) + 1 (C-C) + 1 (C≡N) + 1 (C≡N) = 4
- π bonds = 2 + 2 = 4
- Conclusion: 6 σ bonds and 4 π bonds (not equal).

#### Option 3: HCO₃⁻
- Structure: H - C(=O) - O⁻ - O
- Bonds:
- H - C has 1 σ bond.
- C=O has 1 σ bond and 1 π bond.
- C-O⁻ has 1 σ bond.
- Total:
- σ bonds = 1 (H-C) + 1 (C=O) + 1 (C-O) = 3
- π bonds = 1 (C=O) = 1
- Conclusion: 4 σ bonds and 1 π bond (not equal).

#### Option 4: XCO₄
- Structure: O=C(O) - O - O
- Bonds:
- Each double bond has 1 σ bond and 1 π bond.
- Total:
- σ bonds = 1 (C=O) + 1 (C=O) + 1 (C=O) + 1 (C=O) = 4
- π bonds = 1 + 1 + 1 = 4
- Conclusion: 4 σ bonds and 4 π bonds (equal).

### Final Answer
The species with equal numbers of sigma and pi bonds is **Option 4: XCO₄**.