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 
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Answer:
V = 16.81 L
Explanation:
Given data:
Number of moles = 0.75 mol
Temperature = standard = 273 K
Pressure = 1 atm
Volume of balloon = ?
Solution:
The given problem will be solve by using general gas equation,
PV = nRT
P= Pressure
V = volume
n = number of moles
R = general gas constant = 0.0821 atm.L/ mol.K
T = temperature in kelvin
Now we will rearrange the formula.
V = nRT/P
V = 0.75 mol ×0.0821 atm.L/mol.K ×273 K / 1 atm
V = 16.81 atm.L/ 1 atm
V = 16.81 L
Molar mass of FE2O3=2(55.85)+3(16)=159.7
2.56g*1mol/159.7*2mol/1mol*55.85g/1mol=1.79g