Question

An element was burnt in limited supply of air to give oxide A which on treatment with water gives an acid B. Acid B on oxidation gives acid C which gives yellow precipitate with AgNO3. Identify A

Answer 1

An element is burnt in limited supply of air to give an oxide A, which on treatment with water gives an acid B. Acid B on heating gives acid C which gives yellow precipitate with silver nitrate solution. Oxide A is P2O3 

Answer 2

Answer is P2O3 - Diphosphorus trioxide or Phosphorous oxide.

Explanation:

When Phosphorous is heated in a limited supply of air (oxygen), it forms Phosphorous oxide.

Phosphorous oxide gives phosphorous acid when treated with water.

When Phosphorous acid is oxidized, it gives Phosphoric acid and upon reaction with AgNO3, a yellow precipitate is formed.

Hope it helps.