A vendor bought lemons at 7 for ₹1.

Cost price of 7 lemons = ₹1
C.P. of 1 lemon = $ \frac{1}{7} $
Gain = 40%
Required S.P. of 1 lemon = $ \frac{1}{7}\times\frac{140}{100}=\frac{1}{5} $
If S.P. of 1 lemon $ =\frac{1}{5}, \text{ then lemons sold for ₹1} = 5 $
Answer = 5