Reaction between following pairs will produce hydrogen except :

Options

A. `Cu + HCl`
B. `Fe+H_(2)O(g)`
C. `Mg+H_(2)O`(hot)
D. `Na` + Alcohol

Explanation

To solve the question regarding which pair of reactants will not produce hydrogen gas, we will analyze each given pair systematically.

### Step-by-Step Solution:

1. **Identify the Reactants**: The first pair is Copper (Cu) and Hydrochloric acid (HCl).

2. **Check Reactivity**: Look at the reactivity series of metals. In the reactivity series, metals are arranged based on their ability to displace hydrogen from acids. Hydrogen is above copper in the reactivity series.

3. **Determine the Reaction**: Since copper is less reactive than hydrogen, it cannot displace hydrogen from hydrochloric acid. Therefore, the reaction between Cu and HCl will not produce hydrogen gas.

4. **Evaluate the Next Pair**: The second pair is Iron (Fe) and Water (H2O). When iron reacts with steam (water in gaseous form), it can produce iron oxide (Fe3O4) and hydrogen gas.

5. **Evaluate the Third Pair**: The third pair is Magnesium (Mg) and hot water. Magnesium reacts with hot water to form magnesium hydroxide (Mg(OH)2) and hydrogen gas is also produced.

6. **Evaluate the Fourth Pair**: The fourth pair is Sodium (Na) and Alcohol (ROH). Sodium reacts with alcohol, displacing hydrogen and forming sodium alkoxide (RONa) and hydrogen gas.

7. **Conclusion**: After analyzing all pairs, only the reaction between Copper and Hydrochloric acid does not produce hydrogen gas.

### Final Answer:
The pair that will not produce hydrogen gas is **Copper (Cu) and Hydrochloric acid (HCl)**.

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