$\mathrm { X }$ -Rays of Wavelength $0.20 \mathrm {~nm}$ Are Scattered by a Free Electron

Multiple Choice

$\mathrm { X }$ -rays of wavelength $0.20 \mathrm {~nm}$ are scattered by a free electron. The change in the wavelength of the x-rays is observed to be $2.0 \times 10 ^ { - 12 } \mathrm {~m}$ at a certain scattering angle measured relative to the incoming x-ray direction. What is the scattering angle of the $x$ -rays? $\left( m _ { \text {electron } } = 9.11 \times 10 ^ { - 31 } \mathrm {~kg} \right.$ , $\left. c = 3.00 \times 10 ^ { 8 } \mathrm {~m} / \mathrm { s } , h = 6.626 \times 10 ^ { - 34 } \mathrm {~J} \cdot \mathrm { s } \right)$

A) $60 ^ { \circ }$
B) $40 ^ { \circ }$
C) $20 ^ { \circ }$
D) $80 ^ { \circ }$