Correct Answer - Option 1 : 15 cm
As per IS 1742, 1983, the minimum dia of sewer recommended is 100 mm, since it is not given in option, so the next higher value of dia recommend ed is 150 mm is the most appropriate.
Other Provisions:
1. The sewer shall be designed for discharging three times the dry-weather flow flowing half-full with a minimum self-cleansing velocity of 0.75 m/s.
2. The minimum gradient for laying sewer is 1 in 57. (For 100 mm dia pipe).
3. Manning’s N to be considered while designing of sewers to be 0.015.
