Which of these reactions will not produce hydrogen gas as a by-product?

Options

A. Reaction of zinc with oxygen.
B. Reaction of sodium with water.
C. Reaction of zinc with sodium hydroxide.
D. Reaction of iron with dilute hydrochloric acid.

Answer

To determine which of the given reactions will not produce hydrogen gas as a by-product, we will analyze each reaction step by step.

### Step 1: Analyze the Reaction of Zinc with Oxygen
- **Reaction:** Zinc (Zn) + Oxygen (O₂) → Zinc Oxide (ZnO)
- **Products:** The products of this reaction are zinc oxide (ZnO).
- **Hydrogen Gas Production:** There is no hydrogen gas produced in this reaction.

### Step 2: Analyze the Reaction of Sodium with Water
- **Reaction:** Sodium (Na) + Water (H₂O) → Sodium Hydroxide (NaOH) + Hydrogen Gas (H₂)
- **Products:** The products of this reaction are sodium hydroxide (NaOH) and hydrogen gas (H₂).
- **Hydrogen Gas Production:** Hydrogen gas is produced in this reaction.

### Step 3: Analyze the Reaction of Zinc with Sodium Hydroxide
- **Reaction:** Zinc (Zn) + Sodium Hydroxide (NaOH) → Sodium Zincate (Na₂ZnO₂) + Hydrogen Gas (H₂)
- **Products:** The products of this reaction are sodium zincate (Na₂ZnO₂) and hydrogen gas (H₂).
- **Hydrogen Gas Production:** Hydrogen gas is produced in this reaction.

### Step 4: Analyze the Reaction of Iron with Dilute Hydrochloric Acid
- **Reaction:** Iron (Fe) + Dilute Hydrochloric Acid (HCl) → Iron(II) Chloride (FeCl₂) + Hydrogen Gas (H₂)
- **Products:** The products of this reaction are iron(II) chloride (FeCl₂) and hydrogen gas (H₂).
- **Hydrogen Gas Production:** Hydrogen gas is produced in this reaction.

### Conclusion
After analyzing all four reactions, we find that:
- The reaction of zinc with oxygen does not produce hydrogen gas as a by-product.
- The other three reactions (sodium with water, zinc with sodium hydroxide, and iron with dilute hydrochloric acid) all produce hydrogen gas.

Thus, the correct answer is **the reaction of zinc with oxygen**.