Answer
Calculating the mass number for an atom requires that we know the atomic number and the number of protons in the atom’s nucleus. The mass number then gives us the average weight of atoms of a given element. However, as long as the number of protons equals the number of neutrons, the values balance out and we always obtain a whole number for the mass number.
Explanation:
those 3
D as it only has a negative effect when being used and it is small at that anyway.
Answer: Balanced equation that is formed by combining these two half reactions is
.
Explanation:
A chemical equation which contains same number of atoms on both reactant and product side is called a balanced chemical equation.
For example, 

On cancelling the common species from both these half-reactions, the complete balanced equation will be as follows.
Thus, we can conclude that balanced equation that is formed by combining these two half reactions is
.