Chemicals A and B each initially at `20^(@)C` react exothermically. A graph of the final temperature reached by mixing equimolar solutions of A and B to a total of `100 mL` is given below. According to this graph, in what mole ratio does A and B react ?
A. `2 :1`
B. `3:1`
C. `4:1`
D. `3:2`
