Answer:
a) 
b) infrared region
Explanation:
Photon energy is the "energy carried by a single photon. This amount of energy is directly proportional to the photon's electromagnetic frequency and is inversely proportional to the wavelength. If we have higher the photon's frequency then we have higher its energy. Equivalently, with longer the photon's wavelength, we have lower energy".
Part a
Is provide that the smallest amount of energy that is needed to dissociate a molecule of a material on this case 0.42eV. We know that the energy of the photon is equal to:

Where h is the Planck's Constant. By the other hand the know that
and if we solve for f we have:

If we replace the last equation into the E formula we got:

And if we solve for
we got:

Using the value of the constant
we have this:


Part b
If we see the figure attached, with the red arrow, the value for the wavelenght obtained from part a) is on the infrared region, since is in the order of 
Answer:
The answer to your question is given below
Explanation:
From the question given above, we can see that the wave with a higher frequency has a shorter wavelength while that with a lower frequency has a longer wavelength. This is so because the frequency and wavelength of a wave has inverse relationship. This can further be explained by using the following formula:
Velocity = wavelength x frequency
Divide both side by wavelength
Frequency = Velocity /wavelength
Keeping the velocity constant, we have:
Frequency ∝ 1 / wavelength
From the above illustration, we can see clearly that the frequency and wavelength are in inverse relationship. This implies that the higher the frequency, the shorter the wavelength and the shorter the frequency, the higher the wavelength.