Carbon tetrachloride (CCl4) may be produced when reacting excess chlorine with methane. in a beaker
in the presence of light
in a dark room
spontaneously

The correct answer is:   [a]:   the "stratosphere" .

So the main goal for the elements is stability which is a complete/full valence shell and typically the magic number for a stable element is 8 valence electron but not always. so elements to the left of the periodic table tend to be way less stable then those on the right, so the elements on the left are much more reactive.