A mixture of hydrazine and ……. With a copper (II) catalyst is used as rocket propellant.

Answer

**Step-by-Step Solution:**

1. **Identify the Components**: The question states that a mixture of hydrazine and another substance is used as a rocket propellant with a copper (II) catalyst. We need to identify the missing substance.

2. **Recall the Common Rocket Propellants**: In rocket propulsion, various combinations of chemicals are used. One well-known combination is hydrazine (N2H4) and hydrogen peroxide (H2O2).

3. **Determine the Missing Substance**: Given that hydrazine is mentioned, we can deduce that the missing substance in the mixture is hydrogen peroxide (H2O2). This is a common oxidizer used in combination with hydrazine.

4. **Understand the Role of the Catalyst**: Copper (II) catalyst (Cu2+) is used to facilitate the reaction between hydrazine and hydrogen peroxide, enhancing the efficiency of the propellant.

5. **Conclusion**: Therefore, the complete mixture used as a rocket propellant is hydrazine (N2H4) and hydrogen peroxide (H2O2) with a copper (II) catalyst.

**Final Answer**: A mixture of hydrazine and hydrogen peroxide (H2O2) with a copper (II) catalyst is used as rocket propellant.

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