ANS:C - 90°

The value of the included angle of a triangular notch for maximum discharge is 90°. A triangular notch is a common type of weir used in open-channel flow measurement. The triangular notch is formed by two converging plates, creating a triangular opening through which the fluid flows. The angle formed at the apex of the notch is known as the included angle. For a triangular notch, the angle that yields the maximum discharge (i.e., the maximum flow rate of water over the weir) is approximately 90°. This angle is often used in practical applications to design triangular notches for efficient flow measurement.