Which of the following is true of both nuclear fusion and nuclear fission?
a.
they both require a high energy input.
b.
they both occur without byproducts.
c.
they both have a high energy output.
d.
they both involve large atoms breaking into smaller atoms.

c. They both have a high energy output.

Explanation:

- Nuclear fusion is the process in which two lighter nuclei combine together into a heavier nucleus

- Nuclear fission is the process in which a heavier nucleus breaks apart into smaller nuclei

In both cases, a huge amount of energy is released. In fact:

- In the nuclear fusion, the mass of the heavier nucleus is slightly lower than the sum of the masses of the two initial nuclei: this means that part of the initial mass has been converted into energy, according to the equation

and we can see that even for small amount of mass, m, the energy released is huge

- In the nuclear fission, the mass of the final products is less than the mass of the initial heavier nucleus, so again, part of the initial mass has been converted into energy, according to the equation

a.  They both require a high energy input.  No.  Fission doesn't require ANY energy input to get going.  

b.  They both occur without byproducts.   No.  The by-products of fission are the biggest real problem in commercial nuclear power . . . where to put the bad stuff that's left over.

c.  They both have a high energy output.  Yes !

d.  They both involve large atoms breaking into smaller atoms.  No.  'Fission' involves large nucleii breaking into smaller ones.  'Fusion' is exactly the opposite ... combining small nucleii into more complex ones.