Hailstones form when raindrops freezes that is from liquid state to solid state.
Hope you got your answer!
I attached the full question.
We need to calculate the enthalpy change first:

Keep in mind this is the energy per mole, we need energy per atom:

We can see that this reaction needs the energy to get started (enthalpy change is positive).
The energy of a photon is given with this formula:

We need this photon to have the same energy (or higher) as our enthalpy change:

This wavelenght is clasified as near infrared.
You first need to convert the hours into minutes, then use the speed equals distance over time formula.
There are two main points that should be emphasized about the different types of electromagnetic radiation. The sequence from longest wavelength (radio waves) to shortest wavelength (gamma rays) is also a sequence in energy from lowest energy to highest energy
hope this helps you!✌