No, it is not accurate: Chemical properties of helium - Health effects ofhelium. Gaseous chemical element, symbol: He, atomic number: 2 and atomic weight 4,0026 g/mol. Helium is one of the noble gases of group O in the periodic table.
Percent by mass of an element can be calculated as
(Total mass of the element in the formula / formula weight ) * 100
Step 1 : Find formula weight of NaHCO₃
To find formula weight of NaHCO₃, we have to add atomic masses of the elements Na, H,C and O
Formula weight of NaHCO₃ = 
Formula weight of NaHCO₃ = 
Formula weight of NaHCO₃ is 84.01 g
Step 2 : Use percent by mass formula
Percent by mass of oxygen = (total mass of oxygen / formula weight) * 100
Percent by mass of oxygen = 
Percent by mass of oxygen = 57.14%
Answer : percentage by mass of oxygen in a formula unit of sodium hydrogen carbonate (NaHCO3) is 57.14%
Answer:
To get number of neutrons, you must have the mass number and atomic number of that atom.

atomic number is number of protons