Chemical reaction is the final part of the sentence

b) 3A  + 2B   →   C

Explanation:

In given ratios of substances there are three mole of reactant A two moles of reactant B and one mole of product C are present.

A : B     3 : 2                          A : C     3 :  1             B : C        2  :  1

So from given information option b is correct.

3A  + 2B   →   C

Here in this equation three moles of A , two moles of B and one mole of C are present.

Other options are incorrect because,

a) 6A  + 6B   →   2C

In this chemical equation six moles of A six moles of B and two mole of C are present. So it is incorrect.

c) A + 2B →   3C

In this chemical equation one mole of A two mole of B and three moles of C are present. So it is incorrect.

d) A + B →   C

In this chemical equation one mole of A one mole of B and one mole of C are present. So it is incorrect.