Answer
The wavelength is $~~6.04~pm$
Work Step by Step
We can find $\Delta \lambda$:
$\Delta \lambda = \frac{h}{mc}~(1 - cos~\phi)$
$\Delta \lambda = \frac{6.63\times 10^{-34}~J~s}{(9.109\times 10^{-31}~kg)(3.0\times 10^8~m/s)}~(1 - cos~120^{\circ})$
$\Delta \lambda = 3.64\times 10^{-12}~m$
We can find the new wavelength:
$\lambda_f = (2.40~pm)+(3.64\times 10^{-12}~m)$
$\lambda_f = 6.04~pm$
The wavelength is $~~6.04~pm$
