Hello i have a question. Sir how can take smaller loop area if flux is being asked over the bigger loop? And in the denominator why have radius of bigger loop is considered if current is flowing in the samller loop?? Were you just concerned in having the correct option? Dont you the question is wrong as it should be the current flowing in bigger flux should have been asked over the samller loop??? Because we can't use this formula for the flux over the bigger loop as magnetic field wont be same everywhere on the area of the bigger loop....