What is the mole ratio of d to a in the generic chemical reaction 2a+b-- c+3d?

 D : A is 3 : 2.

Explanation:

The law of definite proportion is being used here. The law states that a given compound always has the same proportion of its constituent elements by mass.  

2a + b = c + 3d

This actually means that, two moles of “a” react with a mole of “b” to produce a mole of “c” and 3 moles of “d”

Using the concept of stoichiometry coefficients of d and a  

d:a = 3:2

1 a

2 d

3 a

4 c

explanation:

they are all solids.