Answer
$\lambda = 1.2\times 10^{-14}~m$
Work Step by Step
We can find the energy of each photon:
$E = m~c^2$
$E = (207)(9.1\times 10^{-31}~kg)(3.0\times 10^8~m/s)^2$
$E = 1.695\times 10^{-11}~J$
We can find the wavelength of each photon:
$E = \frac{hc}{\lambda}$
$\lambda = \frac{hc}{E}$
$\lambda = \frac{(6.626\times 10^{-34}~J~s)(3.0\times 10^8~m/s)}{1.695\times 10^{-11}~J}$
$\lambda = 1.2\times 10^{-14}~m$
