For $2 \mathrm{A}\to \mathrm{B},\left[\mathrm{A}\right]$ changed from $0.08\mathrm{M}$ to $0.04\mathrm{M}$ in 100 seconds. Now $\frac{\Delta \left[\mathrm{B}\right]}{\Delta \mathrm{t}}$ will be

$2\mathrm{A}\to \mathrm{B}$

Clearly if 2 moles of A react 1 mole B termed So rate iv half of A tor B

$$\begin{gathered} \frac{\mathrm{\Delta B}}{\mathrm{\Delta t}}=\frac{1}{2}=\frac{\mathrm{\Delta A}}{\mathrm{\Delta t}}=\frac{1}{2}\times \frac{0.04}{100} \\ =2\times {10}^{-4} \end{gathered}$$