So this reaction and this reaction, they are both second order. The only difference is we have a single reactant here but we have two reactants here. In this particular case if we double A, then we quadruple the velocity because two to the power of two gives us four. But in this case by doubling A we essentially double v if everything else is kept constant. But if we double A and B and we keep K constant then we quadruple the value of v and finally we can also have 0th order. And in the 0th order basically the concentration of the reactant has no effect on the rate of that reaction.