Question

Which of the following are reducing bleaching agents?
A. Sodium hydrosulphite
B. Sodium bisulphite
C. Sodium perborate
D. Sodium hydroxide
Choose the correct answer from the options given below:

• A. A, B only
• B. B, C only
• C. C, D only
• D. A, D only

Hint:

Bleaching Agents:
Reducing Bleaches = Sodium hydrosulphite (Hydros), Sodium bisulphite.
Oxidizing Bleaches = Hydrogen peroxide ($ ext{H}_2 ext{O}_2$), Sodium hypochlorite, Sodium perborate.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Chemical bleaches decolorize natural pigments via oxidation (nascent oxygen) or reduction (nascent hydrogen/sulfite).

Step 2: Detailed Explanation:
Classification of chemical textile bleaches:
1. Reducing Bleaches (Sulfur-based): Work by removing oxygen from or adding hydrogen to chromophores. Major examples include Sodium hydrosulphite ($\text{Na}_2\text{S}_2\text{O}_4$) and Sodium bisulphite ($\text{NaHSO}_3$). Preferred for animal protein fibres (wool, silk).
2. Oxidizing Bleaches: Release nascent oxygen (e.g., Sodium perborate, Hydrogen peroxide, Sodium hypochlorite).
3. Sodium hydroxide: Caustic alkali used in scouring/mercerization, not a bleach.
Thus, A and B only are reducing bleaching agents.

Step 3: Final Answer:
Hence, the reducing bleaching agents are A, B only, corresponding to option (A).