ANS:A - The water supply pipes carry pure water free from solid particles

1. true in theory. Water supply pipes are designed to transport potable water from its source to consumers. However, it's essential to note that while the water supplied is expected to be free from solid particles, it may still contain dissolved minerals or chemicals depending on its source and treatment process.
2. The water supply pipes get clogged if flow velocity is less than self-cleansing velocity: This statement is accurate. Water supply pipes require a minimum flow velocity, known as the self-cleansing velocity, to prevent the accumulation of sediments, debris, or biofilm on the pipe walls. If the flow velocity drops below this threshold, particles may settle, leading to reduced flow rates, increased friction, and potential clogging of the pipes.
3. The sewers may be carried up and down the hills and valleys: This statement is true. Sewer systems are designed to transport wastewater, including sewage and stormwater runoff, from various sources to treatment facilities or discharge points. Sewers are often laid out following the natural topography of the terrain, which may involve traversing hills and valleys. Proper engineering and design considerations are necessary to ensure efficient flow and prevent issues such as sewage backup or hydraulic overload.
4. The sewer pipes are generally laid along level hills: This statement is inaccurate. Sewer pipes are not typically laid along "level hills" as stated. Instead, sewer systems are designed with proper slope gradients to facilitate the flow of wastewater by gravity. Sewer pipes are laid with a specific slope to ensure that sewage flows smoothly toward treatment plants or disposal points without the need for excessive pumping.
5. None of these: This option implies that none of the statements provided are correct. However, as discussed above, statement (2) regarding water supply pipes and their susceptibility to clogging if the flow velocity falls below the self-cleansing velocity is indeed accurate.

The correct statement from the options provided is: The water supply pipes get clogged if flow velocity is less than self-cleansing velocity. Water supply pipes indeed risk becoming clogged if the flow velocity falls below the self-cleansing velocity. This velocity ensures that sediment and other particles do not settle within the pipes, maintaining water quality and flow efficiency. If the flow velocity drops too low, sedimentation and deposition can occur, leading to reduced water quality and potential clogging of the pipes. Therefore, maintaining an adequate flow velocity is crucial for the proper functioning of water supply systems.