Chlorine gas is widely used in industry for the manufacture of which common chemical product?

Introduction / Context:
This question checks your knowledge of important industrial uses of chlorine gas, which is a highly reactive and widely used chemical in inorganic chemistry and everyday life. Knowing which common products are made using chlorine helps you connect textbook chemistry to real industrial applications such as water treatment, disinfection, and manufacturing of cleaning agents.

Given Data / Assumptions:

• Reactant of interest: chlorine gas Cl2.
• We are asked about manufacture of a common compound used in households or industry.
• Options include baking powder, bleaching powder, baking soda, washing soda and caustic soda.
• Assume standard large scale industrial processes.

Concept / Approach:
Chlorine gas is a strong oxidising agent. It is used in many processes, including water chlorination and production of various chlorine containing compounds. Bleaching powder is chemically calcium oxychloride, often written as CaOCl2 or more precisely Ca(OCl)Cl. It is produced industrially by passing chlorine gas over dry slaked lime Ca(OH)2. On the other hand, compounds like baking soda and washing soda are usually produced by processes such as the Solvay process, which do not use chlorine gas as the main reactant. Therefore, we identify which product in the options clearly uses chlorine gas in its manufacturing route.

Step-by-Step Solution:
Step 1: Recall the chemical formula and preparation of bleaching powder. Step 2: Bleaching powder is essentially calcium oxychloride, produced by the reaction of chlorine gas with dry slaked lime. Step 3: The simplified reaction is: Ca(OH)2 + Cl2 → CaOCl2 + H2O. Step 4: In this process chlorine gas is a key reactant, so bleaching powder is directly linked to the industrial use of chlorine. Step 5: Baking soda (sodium hydrogen carbonate, NaHCO3) and washing soda (sodium carbonate, Na2CO3) are prepared mainly via the Solvay process from sodium chloride, ammonia and carbon dioxide, not from chlorine gas itself. Step 6: Baking powder is a mixture containing baking soda and an acid salt, and is not manufactured by direct reaction with chlorine gas. Step 7: Caustic soda (sodium hydroxide) is produced mainly by electrolysis of brine rather than by direct reaction of chlorine gas with a base in this context.

Verification / Alternative check:
A simple memory check is that bleaching powder is associated with chlorine both in name and in use. It is widely used for bleaching cloth, paper and for disinfecting water, all processes that rely on the oxidising power of chlorine. In textbooks the preparation of bleaching powder from slaked lime and chlorine is a standard example in the chapter dealing with chlorine and its compounds, which confirms that the correct product is bleaching powder.

Why Other Options Are Wrong:
Baking powder is a mixture of baking soda and acid salts and is not directly manufactured using chlorine gas. Baking soda and washing soda are sodium carbonate based compounds produced mainly by the Solvay process, where chlorine does not act as a main reactant. Caustic soda is produced industrially by electrolysis of brine, which also produces chlorine and hydrogen as by products, but the question clearly asks for a compound manufactured using chlorine gas, and bleaching powder is the direct example given in textbooks.

Common Pitfalls:
Students sometimes confuse the role of sodium chloride and chlorine gas. While sodium chloride contains the chloride ion, it is not the same as free chlorine gas. Another confusion arises between bleaching powder and bleaching agents in general. Some may mistakenly think of washing soda or baking powder as bleaching agents, but in school chemistry bleaching powder is the classic chlorine based compound. Carefully reading the phrase used in the manufacture helps avoid these mix ups.

Final Answer:
Chlorine gas is widely used in industry to manufacture bleaching powder, a common disinfectant and bleaching agent.