Which of the following is a balanced chemical equation?

Options

A. `H_2+Cl_2to 4HCl`
B. `Zn + 2HCl to ZnCl_2 + H_2`
C. `KNO_3 to KNO_2 + O _2`
D. ` ZnCO_3 to ZnO + 2CO_2`

Explanation

To determine which of the given chemical equations is balanced, we need to analyze each equation and count the number of atoms of each element on both sides of the equation. A balanced chemical equation has the same number of each type of atom on both the reactant and product sides.

### Step-by-Step Solution:

1. **Identify the Equations**: We are given four equations. We will evaluate each one to check for balance.

2. **Evaluate Equation 1**:
- **Equation**: H₂ + Cl₂ → 4 HCl
- **Reactant Side**:
- H: 2 (from H₂)
- Cl: 2 (from Cl₂)
- **Product Side**:
- H: 4 (from 4 HCl)
- Cl: 4 (from 4 HCl)
- **Conclusion**: The number of H and Cl atoms is not equal on both sides. **Not balanced**.

3. **Evaluate Equation 2**:
- **Equation**: Zn + 2 HCl → ZnCl₂ + H₂
- **Reactant Side**:
- Zn: 1
- H: 2 (from 2 HCl)
- Cl: 2 (from 2 HCl)
- **Product Side**:
- Zn: 1 (from ZnCl₂)
- H: 2 (from H₂)
- Cl: 2 (from ZnCl₂)
- **Conclusion**: The number of Zn, H, and Cl atoms is equal on both sides. **Balanced**.

4. **Evaluate Equation 3**:
- **Equation**: KNO₃ → KNO₂ + O₂
- **Reactant Side**:
- K: 1
- N: 1
- O: 3 (from KNO₃)
- **Product Side**:
- K: 1 (from KNO₂)
- N: 1 (from KNO₂)
- O: 3 (2 from KNO₂ and 1 from O₂)
- **Conclusion**: The number of K and N atoms is equal, but O has 3 on the reactant side and 3 on the product side. **Balanced**.

5. **Evaluate Equation 4**:
- **Equation**: ZnCO₃ → ZnO + 2 CO₂
- **Reactant Side**:
- Zn: 1
- C: 1 (from CO₃)
- O: 3 (from CO₃)
- **Product Side**:
- Zn: 1 (from ZnO)
- C: 2 (from 2 CO₂)
- O: 5 (1 from ZnO and 4 from 2 CO₂)
- **Conclusion**: The number of C and O atoms is not equal on both sides. **Not balanced**.

### Final Conclusion:
The only balanced chemical equation from the options provided is **Equation 2**: Zn + 2 HCl → ZnCl₂ + H₂.