Tripling the wavelength of the radiation from a monochromatic source will change the energy content of the individually radiated photons by what factor

By a factor of 1/3.

Explanation:

For a photon with wavelength λ, the energy is written as:

E = h*c/λ

where:

h is the Planck's constant:

h = 6.63*10^(-34) Js

c is the speed of light:

c = 3*10^8 m/s

Now, if we triple the wavelength of this photon, then the energy will be:

E' = (h*c)/(3*λ)

We rewrite this as:

E' = (1/3)*(h*c/λ)

And (h*c/λ) was the previous energy:

(h*c/λ) = E

Then we can replace that in the above equation to get:

E' = (1/3)*(h*c/λ) = (1/3)*E

Then if we triple the wavelength, it will change the energy content of the individually radiated photons by a factor of 1/3.

battery with hi vtge high val resist in series