Correct Answer - b
If the length of the wire between the two bridges is l,
then the frequecy of vibration is
`n=1/(2l)sqrt(T/m)=1/(2l)sqrt(T/(pir^(2)d))`
If the length and diameter `(="radius"/2)` of the wire are
doubled keeping the tension same, then new fundamental
frequency will be `n/4`.