The Ilbert Bill controversy was related to the:

The Ilbert Bill (1883) was introduced by Courtenay Ilbert, Law Member in Lord Ripon's Viceroy's Council, to remove the racial bar that stopped Indian judges and magistrates from trying Europeans. European non-officials reacted sharply, and the government settled in 1884 with a compromise that let a European accused claim a jury with a European majority. So C is correct.

Why the others are wrong:

• A: Restrictions on carrying arms came through the Arms Act of 1878, which regulated licensing of weapons. It has nothing to do with the Ilbert Bill.
• B: Curbs on vernacular newspapers came through the Vernacular Press Act of 1878 under Lytton. That is a separate episode from 1883.
• D: Abolition of the cotton cloth duty was a tariff decision taken in 1882 under Ripon. It is unrelated to the Ilbert controversy.

The core concept is racial equality in criminal justice under colonial rule. The bitter reaction to the bill showed how race shaped colonial politics and helped push Indians toward organised political mobilisation, a useful thread for Mains answers on the colonial state and the rise of the Congress.

Trap: aspirants mix up Ilbert with the Vernacular Press Act or the Arms Act because all three are 1878–83 colonial measures and are often taught together.