four times its first value
a half of its first value
unaltered
a quarter of its first value

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Imagine that the magnetic field produced by single turn of coil be X. Now this is inversly proportional to the square of the radius of the coil (Use biot savarts law).Now in the second case the radius is exactly halved so it is (1/2) times now. The resultant field will be (1/1/2)^2*X=4X