After two half lives how much of the original material has decayed

Explanation: After 1 half life , clearly HALF of the original isotope remains. And after TWO half-lives, a HALF + HALF of a HALF , i.e. 34 of the original mass has decayed.

I think that you need to divide the quantity of the substance in half twice.

ability to bond woth oxygen

kelp are large brown algae that live in cool, relatively shallow waters close to the shore. they grow in dense groupings much like a forest on land. these underwater towers of kelp provide food and shelter for thousands of fish, invertebrates, and marine mammal species.

e) all of the above