When sulphuric acid is poured over zinc, the gas formed is hydrogen. This reaction is a classic example of a single displacement reaction.

**Reaction Equation:**
Zn + H2SO4 → ZnSO4 + H2

**Explanation:**

1. **Single Displacement Reaction:**
A single displacement reaction, also known as a substitution reaction, occurs when one element displaces another element in a compound. In this reaction, zinc (Zn) displaces hydrogen (H) from sulphuric acid (H2SO4).

2. **Dissociation of Sulphuric Acid:**
Sulphuric acid (H2SO4) is a strong acid that dissociates into hydrogen ions (H+) and sulphate ions (SO4^2-) in water. The dissociation equation is as follows:
H2SO4 → 2H+ + SO4^2-

3. **Reaction between Zinc and Hydrogen Ions:**
When zinc (Zn) is added to sulphuric acid, it reacts with the hydrogen ions (H+) present in the acid. Zinc has a higher reactivity than hydrogen, so it displaces hydrogen from the acid. The reaction can be represented as:
Zn + 2H+ → Zn^2+ + H2

4. **Formation of Zinc Sulphate:**
As a result of the reaction, zinc ions (Zn^2+) combine with sulphate ions (SO4^2-) from sulphuric acid to form zinc sulphate (ZnSO4). The chemical equation for this reaction is:
Zn + H2SO4 → ZnSO4 + H2

5. **Formation of Hydrogen Gas:**
The liberated hydrogen gas (H2) is the gas formed when sulphuric acid is poured over zinc. This gas is released as bubbles during the reaction.

In conclusion, when sulphuric acid is poured over zinc, the gas formed is hydrogen (H2). This occurs due to a single displacement reaction between zinc and hydrogen ions in the acid, leading to the formation of zinc sulphate and the release of hydrogen gas.

∆∆∆ Sulphuric acid => H2SO4
Zinc => Zn

Zn + H2SO4 -----> ZnSO4 + H2