5. If the mass of the reactants are: 10g + 20g, then the mass of the
products must be
O 10g
20g
30g
409

I’d have to say no because without oxygen in the water the fish would all be dead. so if you want to fish for dead fish, pick the ponds with the lowest oxygen concentrations.

Carbon based or cells?

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom. 

It must be measured in k.hope my answer is to you : )