Q1: In a residential colony, sewers of diameters 100 mm, 150 mm and 225 mm were laid with a gradient 1 in 120. Which portion of the sewage system does not choke in due course of time

ANS:C - 225 mm dia.

In a sewage system, the likelihood of choking or blockages depends on several factors, including the diameter of the sewer pipes, the gradient (slope) of the pipes, the flow rate, and the characteristics of the sewage being transported. In this scenario, where sewers of diameters 100 mm, 150 mm, and 225 mm are laid with a gradient of 1 in 120, it's important to consider the hydraulic characteristics of each pipe size. Generally, larger diameter pipes can accommodate higher flow rates and are less prone to blockages compared to smaller diameter pipes. Additionally, pipes laid with a steeper gradient can help maintain a self-cleaning velocity, reducing the likelihood of blockages. Given this, all else being equal, the portion of the sewage system that is less likely to choke in due course of time would be the section with the largest diameter pipes. In this case, the 225 mm diameter pipes are larger and would be less prone to choking compared to the 100 mm and 150 mm diameter pipes. Therefore, the portion of the sewage system that does not choke in due course of time would be the section with 225 mm diameter pipes. So, the correct answer is: "225 mm diameter pipes."