c
(c) Self inductance \(L = {\mu _0}{N^2}A\, /l = {\mu _0}{n^2}lA\)
Where \(n\) is the number of turns per unit length and \(N\) is the total number of turns and \(N = nl\)
In the given question n is same. \(A\) is increased \(4\) times and \(l\) is increased \(2\) times and hence \(L\) will be increased \(8\) times.