In the Compton scattering experiment shown in the figure, a monochromatic beam of X$-$rays strikes a target containing free electrons. Scattered X $-$rays are detected with a wavelength of $2\mathrm{.}50{10}^{-12}m$ at an angle of $45$ away from the original beam direction. What is the wavelength of the incident monochromatic $x-$rays? Note: The mass of an electron is $9\mathrm{.}11{10}^{-31}kg.$

$3\mathrm{.}21{10}^{-12}m$

$2\mathrm{.}03{10}^{-12}m$

$1\mathrm{.}79{10}^{-12}m$

$2\mathrm{.}50{10}^{-12}m$

$2\mathrm{.}86{10}^{-12}m$