In the paper industry, which of the following is commonly used as a bleaching agent for pulp to improve whiteness while reducing the use of elemental chlorine?

Introduction / Context:
Bleaching of wood pulp is an important step in the paper industry to produce bright, white paper. Historically, elemental chlorine was used for bleaching, but environmental concerns have led to the adoption of alternative bleaching agents. This question asks which substance is commonly used to bleach pulp in the paper industry, highlighting the role of oxidising agents in industrial chemistry and environmental protection.

Given Data / Assumptions:

• The context is pulp bleaching in paper manufacturing.
• The aim is to remove colour causing lignin residues while preserving cellulose.
• Modern processes aim to reduce harmful chlorinated by products.
• The options include acids, enzymes, oxidising agents and other chemicals.

Concept / Approach:
Hydrogen peroxide and other peroxide compounds are widely used as bleaching agents in the paper industry. Peroxides act as powerful oxidising agents that can break down coloured lignin structures in pulp without producing as many harmful chlorinated organic compounds as elemental chlorine. They are part of elementary chlorine free or total chlorine free bleaching sequences. Mild sulphuric acid is not a bleaching agent, glucose isomerase is an enzyme used in the food industry, and iodine with water is not used for pulp bleaching. Therefore, peroxide is the correct choice among the options.

Step-by-Step Solution:

Verification / Alternative check:
Industrial chemistry and environmental engineering texts describe several bleaching sequences for pulp, such as peroxide bleaching, ozone bleaching and chlorine dioxide bleaching. Hydrogen peroxide bleaching is often highlighted as an environmentally friendly method since it breaks down into water and oxygen after use. Process flow diagrams for modern paper mills frequently include peroxide stages. Sulphuric acid appears mainly in pH adjustment and not as a primary bleaching agent. Enzymes like xylanases may be used to aid bleaching, but glucose isomerase is not one of them. These points confirm that peroxide compounds are commonly used bleaching agents.

Why Other Options Are Wrong:

• Mild sulphuric acid: Used mainly to adjust pH or in some chemical treatments but not a primary bleaching agent for pulp.
• Glucose isomerase: An enzyme used to convert glucose into fructose in the manufacture of high fructose corn syrup, not used in pulp bleaching.
• Iodine and water: Used as an antiseptic solution for medical purposes, not in bleaching paper pulp.
• Sodium chloride solution: Common salt solution does not bleach pulp; chlorine based bleaching would require chlorine or chlorine dioxide, not simply sodium chloride.

Common Pitfalls:
Students may focus on chlorine related chemicals because of older references to chlorine bleaching in paper manufacture and confuse simple salt solutions with the actual bleaching agents. Another mistake is to assume that any strong acid like sulphuric acid must be effective for bleaching, which is not accurate. Remember that modern environmentally conscious paper mills often advertise elemental chlorine free bleaching and rely on oxidising agents like hydrogen peroxide to achieve high brightness with less pollution.

Final Answer:
In the paper industry, pulp is commonly bleached using Peroxide based bleaching agents such as hydrogen peroxide.