An optically inactive amine $\left(\mathrm{A}\right), {\mathrm{C}}_4{\mathrm{H}}_{11}\mathrm{N}$ on treatment with ${\mathrm{HNO}}_2$ gives an alcohol $\left(\mathrm{B}\right)$. The compound $\left(\mathrm{B}\right)$ on heating with concentrated ${\mathrm{H}}_2{\mathrm{SO}}_4$ at $453 \mathrm{K}$ gives an alkene $\left(\mathrm{C}\right).$ $\left(\mathrm{C}\right)$on treatment with $\mathrm{HBr}$ gives an optically active compound $\left(\mathrm{D}\right)$ having molecular formula ${\mathrm{C}}_4{\mathrm{H}}_9\mathrm{Br}.$ Identify $\left(\mathrm{A}\right)$.