Option (B) is correct
Explanation
Let each wire has got length L and area of cross section A .So the resistance of i th wire will be
Ri = i×L/A, since i th wire has resistivity i
Hence equivalent resistance of the combination will be
R = R1+R2+R3+.......+Rn
= (1+2+3+......+n)×L/A
Again when n - wires are connected in series total length becomes nL but area of cross section remains same . So total resistance becomes
R = r× (n×L)/A, where r is the resistivity of the combination.
Comparing we get
r×n =1+2+3+.....+n
r =[ n(n+1)]/(2n)= (n+1)/2
So option (B) is correct.
