Plutonium isotopes undergo decay, producing heat. plutonium isotope 239 (pu-239) has 1.9 watts per kilogram [w/kg] of decay heat. how much heat, in units of calories [cal], will 1.25 moles [mol] of pu-239 release after decaying for three hours [h]? assume plutonium has a molecular weight of 244 grams per mole [g/mol].

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m