What is the mechanical advantage of a pulley?

Mechanical advantage is the ratio of the load and effort.

Mechanical advantage of a pulley is 1.

Explanation:  

A pulley system will help in reducing the effort when lifting a load. If more pulleys are used, less effort force is required, making the lifting easy.

When only one pulley is used to lift a load, the mechanical advantage is 1.

If the number of pulleys used are increased, less effort can be applied, as the mechanical advantage increases.

The mechanical advantage is equal to the number of ropes passing over the pulley or pulleys to which the load is attached.

The rope along which the effort is applied is not counted.

explanation:

could i give you a exaplo that could you?

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.