PLEASE HELP!

Why is a buffer only effective within a certain pH range?

A concentrated buffer can neutralize more added acid or base than a dilute buffer, because it contains more acid/conjugate base. However, any buffer will lose its effectiveness if too much strong acid or base is added.

"d.) carbon dioxide and hydrogen sulfide"

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.