Final answer:
The number of unique collisions between A and B is equal to the number of moles of A or B.
Step-by-step explanation:
In order to find the number of unique collisions between A and B, we need to use the concept of mole ratios.
Given that we have 1.21 moles of A(g) and 2.10 moles of B(g), we can compare their coefficients in the balanced equation.
Let's assume the balanced equation is A + B -> AB.
Since the coefficients are the same for both A and B, the ratio of their moles is 1:1.
Therefore, the number of unique collisions between A and B is equal to the number of moles of either A or B, which is 1.21 moles or 2.10 moles.