Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: In case of substitute commodities \(X_1\) and \(X_2\), both partial marginal demand of \(\frac{∂X_1}{∂P_2}\) and \(\frac{∂X_2}{∂P_1}\) are positive, where \(\frac{∂X_1}{∂P_2}\) means partial marginal demand of \(X_1\) with respect to \(P_2\) and \(\frac{∂X_2}{∂P_1}\) means partial marginal demand of \(X_2\) with respect to \(P_1\)
Reason R: In case of substitute commodities, increase in price of one of them causes an increase in demand for the other provided the price of the other commodity is held fixed.
In the light of the above statements, choose the correct answer from the options given below.