Some fuel cells are powered by hydrogen scientists are looking into the decomposition of water to make hydrogen fuel with the of the sun's energy what challenge do scientists face with this task
a) decomposing water requires high activation energy
b) the sun isn't a renewable resource
c) decomposing water results in toxic byproducts
d) scientists are uncertain what to do with the excess oxygen

A) Decomposing water requires high activation energy

Explanation:

The sun is a renewable resource, because the solar energy we use is less than the solar energy being created.  Decomposing water produces hydrogen gas and oxygen gas, which aren't toxic.  The oxygen is used in the combustion of the hydrogen gas.  However, splitting water molecules into hydrogen and oxygen takes a lot of energy.

b would be the answer