Nickel carbonyl (IUPAC name: tetracarbonylnickel) is the organonickel compound
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 
Just put 2 in front of NaNO3
You use the equation M1V1=M2V2 for dilution problems
(250)3=.5x
x= 1500 mL
Examples: phosphorus trichloride
( PCl3)
Phosphorus trioxide
( P2O3)