Answer: 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
Keeping in mind law and equation:
2a + b = c + 3d
using the ratio of Stoichiometric coefficients:
This means that from two moles of "a" forms three moles of "d"
So the ratio of d:a is 3:2