Why are metals good conductors of electric current? choose one of the following
do they possess high concentrations of protons
do they possess low concentrations of protons
do they possess high concentrations of free electrons
do they possess low concentrations of free electrons

They possess high concentrations of free electrons

Explanation:

Let's start by explaining that a material is a good electrical conductor when it allows the flow of electric current without much resistance.  

This is achieved because the atoms of which the material is composed, have electrons in their valence shell, which is the outermost layer where the electrons (the particles responsible for transporting electricity) can be easily detached to form atomic bonds, so there is no need of a huge amount of energy for these electrons to jump from one atom to another and form stable chemical bonds.  

This is what happens with metals, because they have an atomic structure so united and stable that when an electric flow passes through it, the electrons in the metal flow unimpeded.

your answer is c! hope this : )

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.