ANS:A - less than 1.0

The flow in an open channel is said to be subcritical if the Froude number is less than 1.0. The Froude number (Fr) is a dimensionless number used to characterize the flow regime in open channels. It is defined as the ratio of the flow inertia to the gravitational forces and is given by the formula: Fr=​V/g⋅d​ Where:

• V is the velocity of the flow,
• g is the acceleration due to gravity, and
• d is the depth of flow.

When the Froude number is less than 1.0, it indicates that the inertia forces dominate over the gravitational forces, resulting in a subcritical flow regime. In this condition, the flow velocity is typically lower, and the flow behaves in a stable manner, with the water surface appearing smooth and gradually varying. Therefore, the correct statement is: The flow in an open channel is said to be subcritical if the Froude number is less than 1.0.