Q1: In septic tanks,

ANS:E - all the above.

In septic tanks, all of the mentioned statements are typical design considerations: a. Free board of 0.3 m may be provided: Freeboard is the vertical distance between the liquid level in the tank and the top of the tank. Providing a freeboard helps prevent overflow and allows for fluctuations in liquid level. b. The baffles or tees are extended up to the top level of scum: Baffles or tees are structures within the septic tank that help to control the flow of wastewater and prevent the disturbance of settled solids. Extending them up to the top level of scum helps optimize the separation process. c. The clear space between the baffle top and covering slab is about 7.5 cm: This space ensures proper ventilation and prevents the accumulation of gases within the tank, which can be hazardous and cause odors. d. The inlet is kept 30 cm below the sewage line, and the outlet is kept at a level 40% depth of the sewage: These inlet and outlet configurations help facilitate proper settling and retention time of solids and allow for the efficient removal of liquid effluent from the tank. Therefore, the correct option is: e. All the above.