Question

workdone in circular loop is

Answer 1

it is zero . 
because the formulae of work done= force x displacement.
 when u complete a full round . actually u travelled some distance but your displacement is zero hence, work done is zero.
displacement means difference between final and initial position which in case of a circular loop is zero.

Answer 2

The work done in circular loop is a function of time if you have constant angular velocity .. IT WOULD be zero when it will start at some point and land at the same point making 0 displacement in other cases it won't be zero . The maximum would be 2R and minimum is 0