The worst case propagation delay in a 4 bit ripple counter is 40 msec. Which one gives correct propagation delay in each flip flop of the counter?

Ripple counter is asynchronous counter, i.e. output of each flip flop is a clock to next flip flop. In 4 bit ripple counter, no. of flip flop is 4. Maximum delay is 40 msec, the delay propagates from first flip flop to last flip flop in 4 clocks. So, the delay from each flip flop is 40/4 = 10 msec. Delay in first flip flop + delay in second flip flop and so on.