The rate of reaction $\mathrm{A}+2\mathrm{B}\to$ Products is given by $-\frac{\mathrm{d}\left[\mathrm{A}\right]}{\mathrm{dt}}=\mathrm{k}\left[\mathrm{A}\right][\mathrm{B}{]}^2$ . If B is present in large excess, the order of reaction is 

When B is present in large excess, rate is indepent of concentration of B thus it is pseudo first order reaction

Rate = K[A]¹. Order of the reaction is 1