Answer:
Im sorry i though this was a joke i don't know I'm sorry:
Answer: D) helium.
Explanation:
Nuclear fission is a process which involves the conversion of a heavier nuclei into two or more small and stable nuclei along with the release of energy.

Nuclear fusion is a process which involves the conversion of two small nuclei to form a heavy nuclei along with release of energy.
Example: 
Thus when deuterium and tritium , the two isotopes of hydrogen are fused, a heavier nuclei helium is being formed from two smaller nuclei releasing a neutron.
Answer:
Pure water has an acidity of about 7 on the pH scale. -is a chemical property of pure water. Pure water has an acidity of about 7 on the pH scale
By direct heating of an element with oxygen : many metals and non-. metals burn rapidly when heated in oxygen or air producing their oxides e.g.
(a)- Time
(b)- Heat produced(i guess)
(c)- Material
this is what I think, hope it helps