Which of the following is a reducing agent ?

Options

A. `NaHCO_(3)`
B. `NaHSO_(3)`
C. `Na_(2)O_(2)`
D. `NaHSO_(4)`

Explanation

To determine which of the given compounds is a reducing agent, we need to analyze the oxidation states of the elements in each compound. A reducing agent is a substance that donates electrons to another substance, reducing it while itself getting oxidized. This means that the reducing agent must be in a lower oxidation state and must be able to be oxidized further.

### Step-by-Step Solution:

1. **Identify the Compounds**: The compounds given are:
- NHCO3 (Sodium bicarbonate)
- NHSO3 (Sodium bisulfite)
- Na2O2 (Sodium peroxide)
- NaHSO4 (Sodium bisulfate)

2. **Calculate the Oxidation States**:
- **NHCO3**:
- The oxidation state of carbon (C) can be calculated as follows:
- NH: +1 (for nitrogen) + HCO3: -1
- Let the oxidation state of C be X.
- +1 + X - 6 = -1 (considering HCO3 has a total charge of -1)
- Therefore, X = +4.
- Since carbon is in its highest oxidation state (+4), NHCO3 cannot act as a reducing agent.

- **NHSO3**:
- The oxidation state of sulfur (S) can be calculated:
- Let the oxidation state of S be Y.
- NH: +1 + Y + 3(-2) = -1 (since there are three O atoms, each with a -2 oxidation state)
- Therefore, +1 + Y - 6 = -1.
- Solving gives Y = +4.
- Sulfur can be oxidized to +6, indicating that NHSO3 can act as a reducing agent.

- **Na2O2**:
- The oxidation state of oxygen (O) in Na2O2 is -1 (since it is in the peroxide form).
- The oxidation state of sodium (Na) is +1.
- Therefore, the oxidation state of oxygen does not allow for further oxidation (it is already in a reduced state), so Na2O2 cannot act as a reducing agent.

- **NaHSO4**:
- The oxidation state of sulfur (S) can be calculated:
- Let the oxidation state of S be Z.
- NH: +1 + Z + 4(-2) = -1.
- Therefore, +1 + Z - 8 = -1.
- Solving gives Z = +6.
- Since sulfur is in its highest oxidation state (+6), NaHSO4 cannot act as a reducing agent.

3. **Conclusion**:
- Out of the four compounds, only **NHSO3** can act as a reducing agent because it has the ability to be oxidized further from +4 to +6.

### Final Answer:
The reducing agent among the given options is **NHSO3**.