Answer: second (2)
The overall reaction order is determined by the exponent of the variable. The exponent in numerator would be plus and the exponent from denominator will be a minus.
In this problem, the exponent of {A} and {B} is 1. You just need to add them all since there is no denominator in this equation. The calculation would be: {A} + {B}= 1+1 = 2
