Question

with a proper explanation .....​

Answer 1

As others pointed out, magnetic field at the centre of a circle of radius a is

B=μ0I2a

If the number of turns is increased to N, the radius decreases to r=a/N.

But now, the number of loops has increased to N, so the contribution to the magnetic field at the centre is now due to N loops.

So, Bnew=μ0N∗I2r=μ0N2I2a

=N2B

Answer 2

1st option is the answer

hope this helps....