What is the ratio of 3 kinds of wheat costing ₹1.20 per kg, ₹1.44 per kg and ₹1.74 per kg. so that the mixture may be worth ₹1.41 per kg?

Observe that 1.41 is just a bit less than 1.44, so, a mix of 1.41 can be made by adding a little of 1.20 to the 1.44 type; however, let us assume that there are other reasons to include the more expensive 1.74 type.

100*1.74 = 174

100*1.44 = 144

1.41*(200 + n) = 318 + 1.2n

0.21n = 36, n ~ 171.4

So one of the myriad of ratios possible could be

171.4 at ₹1.20 per kg : 100 at ₹1.44 per kg : 100 at ₹1.74 per kg

There is no single answer to this question.  A mixture of the 1.74 and the 1.20 varieties could be made to cost 1.41 per kg, if mixed in the ratio 21:33.  A mixture of the 1.44 and 1.20 varieties could be made to cost 1.41 per kg if mixed in the ratio 21:3.  If all three kinds are used, there are an infinite number of ways of doing it.