How many of the following can be used as reducing agents.
coke, carbonmonoxide, hydrogen, potassium, aluminium.

Answer

To determine how many of the given substances can act as reducing agents, we need to understand what a reducing agent is. A reducing agent is a substance that loses electrons and, in the process, reduces another substance. This means that the reducing agent itself gets oxidized.

Let's analyze each of the substances provided:

1. **Coke (Carbon)**:
- Coke is essentially carbon in its elemental form, which has an oxidation state of 0.
- Carbon can be oxidized to a stable oxidation state of +4.
- Since it can lose electrons to achieve this oxidation state, coke can act as a reducing agent.

2. **Carbon Monoxide (CO)**:
- In carbon monoxide, carbon has an oxidation state of +2 (with oxygen at -2).
- Carbon can be oxidized further to +4.
- Therefore, carbon monoxide can also act as a reducing agent.

3. **Hydrogen (H₂)**:
- Hydrogen has an oxidation state of 0 in its diatomic form.
- It can lose one electron to become H⁺ (oxidation state +1).
- Since hydrogen can lose electrons, it can act as a reducing agent.

4. **Potassium (K)**:
- Potassium has an oxidation state of 0 in its elemental form.
- It can lose one electron to become K⁺ (oxidation state +1).
- As potassium can lose electrons, it can also act as a reducing agent.

5. **Aluminium (Al)**:
- Aluminium has an oxidation state of 0 in its elemental form.
- It can lose three electrons to become Al³⁺ (oxidation state +3).
- Thus, aluminium can also act as a reducing agent.

Now, summarizing our findings:
- Coke: Reducing agent
- Carbon Monoxide: Reducing agent
- Hydrogen: Reducing agent
- Potassium: Reducing agent
- Aluminium: Reducing agent

**Conclusion**: All five substances can act as reducing agents.

### Final Answer:
All of the following can be used as reducing agents: coke, carbon monoxide, hydrogen, potassium, and aluminium.

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