Explanation:

Introduction:
In mechanical engineering, drives are used to transmit power from one component to another in a machine or system. These drives can be categorized as rigid drives or flexible drives based on their ability to accommodate misalignments or differences in distance between the driving and driven components.

Rigid Drives:
Rigid drives are designed to transmit power between components that are perfectly aligned and have no relative movement. These drives typically consist of solid components, such as gears or direct couplings, which do not have any flexibility or ability to accommodate misalignments. The power transmission in rigid drives is efficient, but they are not suitable for applications where misalignments or flexibility are required.

Flexible Drives:
Flexible drives, on the other hand, are designed to accommodate misalignments and differences in distance between the driving and driven components. These drives use flexible elements, such as belts, chains, or ropes, to transmit power. The flexibility of these elements allows them to bend and adjust to the misalignments, providing a smooth power transmission even in dynamic conditions.

Belt, Chain, and Rope:
Among the flexible drives, belts, chains, and ropes are commonly used. However, they are not all categorized as rigid drives. The correct answer to the given question is option 'B' - Belt is a flexible drive only.

Belt:
A belt drive uses a flexible belt made of materials like rubber, leather, or synthetic materials to transmit power. The belt is wrapped around pulleys, and the rotation of the driving pulley causes the belt to move, transferring power to the driven pulley. Belt drives are commonly used in applications that require speed reduction, such as in automotive engines or industrial machinery.

Chain:
A chain drive uses a flexible chain made of metal links to transmit power. The chain is wrapped around sprockets, and the rotation of the driving sprocket causes the chain to move, transferring power to the driven sprocket. Chain drives are commonly used in applications that require high torque transmission, such as in motorcycles or bicycles.

Rope:
A rope drive uses a flexible rope made of natural or synthetic fibers to transmit power. The rope is wrapped around grooved wheels or sheaves, and the rotation of the driving wheel causes the rope to move, transferring power to the driven wheel. Rope drives are commonly used in applications that require long-distance power transmission, such as in elevators or cranes.

Conclusion:
In summary, belt, chain, and rope are all examples of flexible drives, but only the belt is a flexible drive. The chain and rope drives also fall under the category of flexible drives, but they are not specifically mentioned in the given options.