The dictionary definiton of light is:
the natural agent that stimulates sight and makes things visible.
I'll paraphrase/give a scientific definition:
Light is made of subatomic particles called photons, which jumps electron shells when they're excited, effecting the electromagnetic spectrum, creating visible light.
Hope this helps. Might not as I'm not perfect on this topic yet.
Elements in group 1-2, 13-18, the number of valence electrons is related to the group number. For example, in the first group, the alkali metals there is one valence electron, however in group 13, there are 3 valence electrons. Valence electrons are also known as the outershell electrons.
Boyle's law
I hope this helps
H+= 10^-14 / [OH-1 = 3.125 * 10^-4 M
pH=-log(H+) = 3.505
Just round it down and your answer = 3.5
