$\begin{aligned} & |\overrightarrow{\mathrm{b}}|=1 \&|\overrightarrow{\mathrm{~b}} \times \overrightarrow{\mathrm{a}}|=2 \\ & (\vec{b} \times \vec{a}) \cdot \vec{b}=\vec{b} \cdot(\vec{b} \times \vec{a})=0 \\ & |(\vec{b} \times \vec{a})-\vec{b}|^2=|\vec{b} \times \vec{a}|^2+|\vec{b}|^2 \\ & =4+1=5\end{aligned}$