Residual chlorine in water is determined by A. Starch iodide method B. Orthotolidine method C. Both (A) and (B) D. None of the above

The correct answer is: C. Both (A) and (B).

Residual chlorine is the amount of chlorine that remains in water after it has been treated. It is used to kill bacteria and other microorganisms in water. There are two main methods for determining residual chlorine in water: the starch iodide method and the orthotolidine method.

The starch iodide method is a simple and inexpensive method that is often used in homes and small businesses. It involves adding a few drops of starch solution to a sample of water and then adding a few drops of iodine solution. If there is residual chlorine in the water, a blue-black color will develop.

The orthotolidine method is a more accurate method that is often used in laboratories and large businesses. It involves adding a few drops of orthotolidine solution to a sample of water and then adding a few drops of a reducing agent. If there is residual chlorine in the water, a yellow color will develop.

Both the starch iodide method and the orthotolidine method are effective methods for determining residual chlorine in water. The choice of method will depend on the specific needs of the user.

Here is a brief explanation of each option:

• Option A: Starch iodide method. The starch iodide method is a simple and inexpensive method that is often used in homes and small businesses. It involves adding a few drops of starch solution to a sample of water and then adding a few drops of iodine solution. If there is residual chlorine in the water, a blue-black color will develop.
• Option B: Orthotolidine method. The orthotolidine method is a more accurate method that is often used in laboratories and large businesses. It involves adding a few drops of orthotolidine solution to a sample of water and then adding a few drops of a reducing agent. If there is residual chlorine in the water, a yellow color will develop.
• Option C: Both (A) and (B). Both the starch iodide method and the orthotolidine method are effective methods for determining residual chlorine in water. The choice of method will depend on the specific needs of the user.
• Option D: None of the above. None of the options are correct.