Which of the following gases get released when dilute sulphuric acid (H₂SO₄) reacts with magnesium (Mg)?

Correct — C. Magnesium stands above hydrogen in the reactivity series, so it displaces hydrogen from a dilute acid.

Mg + H₂SO₄ → MgSO₄ + H₂↑

The gas released is hydrogen, option (c). The salt left in solution is magnesium sulphate.

Why the others are wrong

• (a)
  SO₂ — SO₂ comes from hot concentrated sulphuric acid acting as an oxidising agent, as it does with copper. The stem says dilute, and dilute acid simply gives up its hydrogen.
• (b)
  O₂ — Oxygen is not given off when a metal reacts with an acid. The metal takes the place of hydrogen, so hydrogen is the element set free.
• (d)
  SO₃ — SO₃ would need the sulphate ion to break apart. It stays whole: the sulphur and its oxygen end up together in the salt, MgSO₄.

NCERT Class 10 sums up the reaction as:
metal + dilute acid → salt + hydrogen

It works for metals above hydrogen in the activity series. Magnesium, aluminium, zinc and iron qualify. Copper does not, and gives no bubbles with dilute hydrochloric acid.

In NCERT's activity with dilute hydrochloric acid, magnesium bubbles fastest and heats up most, in the order Mg > Al > Zn > Fe.

The salt is named from the acid: sulphuric acid gives a sulphate, hydrochloric acid a chloride.

Key facts

• Metals above hydrogen in the activity series displace hydrogen from dilute acids.
• Magnesium with dilute sulphuric acid gives magnesium sulphate and hydrogen gas.
• Hot concentrated sulphuric acid acts as an oxidising agent and releases sulphur dioxide.
• Magnesium and manganese release hydrogen even from very dilute nitric acid, which oxidises the hydrogen from other metals to water.

Common traps

• Reading the sulphur in sulphuric acid as a clue and choosing SO₂ or SO₃.
• Ignoring the word dilute, when the concentrated acid gives different products.

No directly related past PYQ was found.