Dihydrogen of high purity (> 99.95%) is obtained through :

Solution

Chemistry ma’am · 3 steps

For 99.95% hydrogen, ask which method lets nothing but water split: warm Ba(OH)₂ on Ni electrodes.

1. What purity needs. To get hydrogen above 99.95%, only water should break down. Nothing from the electrolyte, the electrodes or the reactants should end up in the gas.
2. Why Ba(OH)2 works. In warm Ba(OH)₂ solution, Ba²⁺ is not reduced, so H₂ forms at the cathode and O₂ at the anode. Nickel does not corrode in alkali, and warming the solution improves its conductivity.

   Cathode: 2H₂O + 2e⁻ → H₂ + 2OH⁻ Anode: 4OH⁻ → O₂ + 2H₂O + 4e⁻

   Method	What it is used for
   (a) Acidified water, Pt electrodes	Bulk (commercial) hydrogen, not the high-purity route
   (b) Warm Ba(OH)₂, Ni electrodes	Only water is split, so the H₂ is more than 99.95% pure
   (c) Brine electrolysis	Making NaOH and Cl₂; H₂ is only a by-product
   (d) Zn + dilute HCl	Laboratory method; gas carries HCl spray and impurities such as H₂S and AsH₃ from commercial zinc

3. So. High-purity dihydrogen comes from the electrolysis of warm Ba(OH)₂ solution using Ni electrodes, option (b).

The idea to keep. Learn the methods for hydrogen as pairs: Zn + dilute HCl in the lab, acidified water or brine for bulk, and warm Ba(OH)₂ with Ni electrodes for purity above 99.95%.

Answer from the NTA final answer key. Solution by PrepWiser.