If a sample has 220 molecules, how may are left after two half-lives?

haploid cells;

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

the answer is lactic acid from anaerobic respiration. the acid in lactic acid is what creates sore and burning muscles. if you think about how acid burns that will give you a clue for questions like this.