ANS:A - Both A and R are true and R is the correct explanation of A

Both the assertion (A) and the reason (R) are true, but the reason (R) is not a correct explanation of assertion (A). Explanation:

• Assertion (A): A freeboard of 0.3 m is provided above the top sewage line in septic tanks.
• Reason (R): It helps to accommodate the scum in the septic tank.

While it is true that a freeboard of 0.3 m (or some specified height) is often provided above the top sewage line in septic tanks, the reason given, which is to accommodate the scum in the septic tank, is not entirely accurate. The primary purpose of providing a freeboard in septic tanks is to allow for a buffer zone or space above the maximum liquid level to prevent overflow or spillage of wastewater during periods of high flow or heavy rainfall. This extra space acts as a safety margin to prevent sewage from escaping the tank and contaminating the surrounding environment. While it's true that the freeboard may also help in accommodating the scum layer, its main function is to provide a safety margin against overflow. Therefore, both assertion (A) and reason (R) are true, but reason (R) does not correctly explain assertion (A). The provision of a freeboard serves multiple purposes, including accommodating fluctuations in sewage levels and preventing overflow, not just accommodating the scum layer.