Which one of the following pairs of substances on reaction will not not evolve `H_2` gas?

Options

A. (a) Iron and `H_(2)SO_(4)(aq)`
B. (b) Iron and steam
C. (c) Copper and HCl(aq)
D. (d) Sodium and ethyl alcohol

Explanation

To determine which pair of substances will not evolve hydrogen gas upon reaction, we can analyze each option provided in the question. Here’s a step-by-step solution:

### Step 1: Analyze the first pair - Iron and H2SO4
- When iron (Fe) reacts with sulfuric acid (H2SO4), the reaction produces ferrous sulfate (FeSO4) and hydrogen gas (H2).
- **Reaction:**
\[ Fe + H2SO4 \rightarrow FeSO4 + H2 \uparrow \]
- **Conclusion:** Hydrogen gas is evolved.

### Step 2: Analyze the second pair - Iron and Steam (H2O)
- When iron reacts with steam (H2O), it produces iron oxide and hydrogen gas.
- **Reaction:**
\[ 3Fe + 4H2O \rightarrow Fe3O4 + 4H2 \uparrow \]
- **Conclusion:** Hydrogen gas is evolved.

### Step 3: Analyze the third pair - Copper and HCN
- Copper (Cu) is less reactive than hydrogen and does not displace hydrogen from its compounds.
- Therefore, when copper reacts with hydrogen cyanide (HCN), no reaction occurs.
- **Conclusion:** No hydrogen gas is evolved.

### Step 4: Analyze the fourth pair - Sodium and Ethyl Alcohol (C2H5OH)
- Sodium (Na) reacts with ethyl alcohol to produce sodium ethoxide and hydrogen gas.
- **Reaction:**
\[ 2Na + 2C2H5OH \rightarrow 2C2H5ONa + H2 \uparrow \]
- **Conclusion:** Hydrogen gas is evolved.

### Final Conclusion
From the analysis, the pair that does not evolve hydrogen gas upon reaction is **Copper and HCN**.

### Answer
**Option C: Copper and HCN will not evolve hydrogen gas.**

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