Here are some rules:
1. The oxidation state of a free element (uncombined element) is zero.2. For a simple (monatomic) ion, the oxidation state is equal to the net charge on the ion.3. Hydrogen has an oxidation state of +1 and oxygen has an oxidation state of −2 when they are present in most compounds.
The oxidation number of Fe in Fe(NO3)2 is +3.
Three things.
1. The answer is 1,276,704
2. Please make sure you show work. Plagiarism-free person.
3. This is a math question. Not a chemistry question.
Answer: The isotope is represented as 
Explanation:
General representation of an element is given as:
where,
Z represents Atomic number
A represents Mass number
X represents the symbol of an element
Atomic number is defined as the number of protons or number of electrons that are present in an atom.
Atomic number = Number of electrons = Number of protons = 7 (for nitrogen)
Mass number is defined as the sum of number of protons and neutrons that are present in an atom.
Mass number = Number of protons + Number of neutrons = 7+8 = 15
Thus the isotope is represented as 