Which of the followings are the applications of common salt ?
(i) It is used as preservative.
(ii) It is used for manufacture of Na metal and $Cl_2$(g) by electrolysis in molten state.
(iii) It is used for manufacture of caustic soda.
(iv) It is used for manufacturing baking soda and washing soda by Solvay process.

Question

Accepted Answer

Option 4, "All of the above," is the correct answer because each of the listed applications of common salt (sodium chloride, NaCl) is indeed valid and widely recognized. Let's examine each statement to understand why they are correct:

1. **(i) It is used as a preservative.**
   - Common salt is extensively used as a preservative in the food industry. It helps in preserving food by drawing out moisture and creating an environment that is inhospitable to bacteria and other microorganisms. This process, known as curing, is commonly used for meats, fish, and pickles.

2. **(ii) It is used for manufacture of Na metal and Cl₂(g) by electrolysis in molten state.**
   - Sodium chloride is used in the industrial production of sodium metal and chlorine gas through the process of electrolysis. When molten NaCl is subjected to electrolysis, it decomposes into sodium metal and chlorine gas. This is a fundamental industrial process for obtaining these elements.

3. **(iii) It is used for manufacture of caustic soda.**
   - Common salt is a key raw material in the production of caustic soda (sodium hydroxide, NaOH). The chlor-alkali process involves the electrolysis of an aqueous solution of sodium chloride (brine), resulting in the production of chlorine gas, hydrogen gas, and sodium hydroxide.

4. **(iv) It is used for manufacturing baking soda and washing soda by Solvay process.**
   - The Solvay process is an industrial method used to produce sodium carbonate (washing soda) and sodium bicarbonate (baking soda) from sodium chloride and limestone (calcium carbonate). This process is one of the most important methods for producing these compounds on a large scale.

Given that all the statements (i), (ii), (iii), and (iv) are accurate and reflect real-world applications of common salt, Option 4, "All of the above," is the correct choice. Each of the other options (1, 2, and 3) excludes one or more of these valid applications, making them incorrect. Therefore, Option 4 is the only option that comprehensively includes all the applications of common salt as listed in the question.