Hydrogen gas is produced when metal reacts with :

Options

A. acid
B. base
C. salt
D. both acid and base

Explanation

To determine when hydrogen gas is produced during the reaction of metals, we can analyze the reactions of metals with acids, bases, and salts. Here’s a step-by-step solution:

### Step 1: Understand the Reactions
- **Metals and Acids**: When a metal reacts with an acid, hydrogen gas is produced. The metal displaces hydrogen from the acid, forming a salt and releasing hydrogen gas.

### Step 2: Example of Metal with Acid
- **Example**: Zinc (Zn) reacting with hydrochloric acid (HCl):
\[ \text{Zn} + 2\text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2 \uparrow \]
- **Conclusion**: Hydrogen gas is produced.

### Step 3: Metals and Bases
- **Metals and Bases**: When a metal reacts with a base, hydrogen gas is also produced. The metal reacts with the hydroxide ion in the base to form a salt and hydrogen gas.

### Step 4: Example of Metal with Base
- **Example**: Zinc (Zn) reacting with sodium hydroxide (NaOH):
\[ \text{Zn} + 2\text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + \text{H}_2 \uparrow \]
- **Conclusion**: Hydrogen gas is produced.

### Step 5: Metals and Salts
- **Metals and Salts**: When a metal reacts with a salt, hydrogen gas is typically not produced. Instead, a more reactive metal can displace a less reactive metal from its salt.

### Step 6: Example of Metal with Salt
- **Example**: Zinc (Zn) reacting with calcium sulfate (CaSO4):
\[ \text{Zn} + \text{CaSO}_4 \rightarrow \text{ZnSO}_4 + \text{Ca} \]
- **Conclusion**: No hydrogen gas is produced.

### Step 7: Final Conclusion
- Hydrogen gas is produced when a metal reacts with both acids and bases, but not with salts. Therefore, the correct answer is that hydrogen gas is produced when metal reacts with acids and bases.

### Final Answer:
Hydrogen gas is produced when a metal reacts with **both acids and bases**.

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