If you added 3ml of 1m naoh to your 100 ml of buffer would it still be a usable buffer according to our conventions?

The disturbance is only parallel to the motion of the wave.

If your on odysseyware i believe the answer would be c. 

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.