Question

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

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

Hint:

Oxidizing bleaches (like hydrogen peroxide or sodium perborate) are more common and permanent.
Reducing bleaches are gentler and often used on protein fibers like wool and silk to avoid fiber damage.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Bleaching agents are chemicals used to remove natural coloring matter and stains from textile fibers.
Based on their chemical mechanism, they are classified as oxidizing bleaching agents (which introduce oxygen to break down chromophores) or reducing bleaching agents (which remove oxygen or add hydrogen).

Step 2: Detailed Explanation:
Let us classify the listed chemicals based on their bleaching mechanism:
- A. Sodium hydrosulphite (Sodium dithionite): A powerful reducing agent widely used in textile processing to strip dyes and bleach fibers.
- B. Sodium bisulphite: A mild reducing agent used to bleach wool and silk, and to remove excess chlorine after chlorine-based bleaching (antichlor treatment).
- D. Sodium thiosulphate: Another reducing agent used as an antichlor treatment to neutralize residual oxidizing bleaches.
Therefore, Sodium hydrosulphite, Sodium bisulphite, and Sodium thiosulphate are reducing bleaching agents.
Conversely:
- C. Sodium perborate: An oxidizing bleaching agent that releases active oxygen when dissolved in hot water.
- E. Potassium permanganate (misspelled as 'Patassium permaganate'): A powerful oxidizing agent used in specialized bleaching processes.
Thus, only A, B, and D are reducing bleaching agents.

Step 3: Final Answer:
The reducing bleaching agents from the list are Sodium hydrosulphite, Sodium bisulphite, and Sodium thiosulphate (A, B and D only).