The fractional form of 2.5% is:

​$$2.5\% \\[6pt]$$​​
​$$2.5\% = \frac{2.5}{100} \\[6pt]$$​​
​$$= \frac{25}{1000} \\[6pt]= \frac{1}{40} \\[6pt]$$​​
Therefore, the correct option is $$\frac{1}{40}.$$​​
Correct answer is (b)