Solved Examples for JEE: Hydrogen | Mock Tests for JEE Main and Advanced 2026 PDF Download

Question 1: The metal X is prepared by the electrolysis of fused chloride. It reacts with hydrogen to form a colourless solid from which hydrogen is released on treatment with water. The metal is
(A) Al
(B) Ca
(C) Cu
(D) Zn
Answer: B
Solution: Calcium is obtained by electrolysis of CaCl₂. Ca reacts with hydrogen to form calcium hydride (CaH₂) which is a colourless solid.
Calcium hydride reacts with water to form calcium hydroxide and dihydrogen gas..
CaCl₂ + H₂ + 2 Na → CaH₂ + 2 NaCl
Hence, the correct option is B.

Question 2: Hydrogen peroxide acts both as an oxidising and as a reducing agent in alkaline solution towards certain first now transitional metal ions. Illustrate both these properties of H₂O₂ using chemical equations.
Solution: As oxidising agent

Question 3: Why hydrated barium peroxide is used in the preparation of H₂O₂ instead of the anhydrous variety? 
Solution: If anhydrous barium peroxide is used in the preparation, the barium sulphate, thus formed forms an insoluble protective coating on the surface of solid barium peroxide. This prevents the further reaction of the acid, i.e., causing the reaction to stop. If, however, hydrated barium peroxide (in the form of this paste) is used, the water causes to dislodge the insoluble. BaSO₄ from the surface of BaO₂. BaSO₄ thus settles at the bottom of the reaction vessle and the reaction continues without any difficulty.