What is the maximum amount by which the wavelength of an incident photon could change when it undergoes compton scattering from an atom or molecule with a 36.0 u mass? (1 u = 1.66 × 10-27 kg)?

You are given an atom or a molecule with a 36.0 u mass. Also you are given 1 u = 1.66 × 10-27 kg. You are asked to find the maximum amount by which the wavelength of an incident photon could change when it undergoes compton scattering from an atom or molecule. 

You will use the formula λ' - λ = Δwavelength = (h/mc) (1 - cosθ)
Since it is the maximum amount of light that can pierce into the atom, use θ = 180°

Δwavelength = (h/mc) (1 - cosθ)
Δwavelength = {6.63 x 10⁻³⁴/[(36.0u)(1.66 x 10⁻²⁷)(3 x 10⁸)]} (1 - cos 180°)
Δwavelength = 7.396 x 10⁻¹⁷m

Letter a, because when there are unlike charges they will always attract to each other.