Theory:

1. Calculate the number of moles in \(46\) \(g\) of sodium.
  
Data:
  
Given mass of sodium \(= 46\) \(g\)
 
Atomic mass or mass number of sodium \(= 23\)
 
Formula:
 
The formula to find the number of moles from the mass is,
 
Numberofmoles=MassoftheelementAtomicmassoftheelement
 
Solution:
 
By substituting the values in the above formula, we get,
 
Numberofmoles=4623=2
 
Hence, the number of moles in \(46\) \(g\) of sodium \(=2\) \(moles\)
  
2. Calculate the number of moles in \(5.6\) \(L\) of oxygen at STP.
  
Data:
  
Given volume of oxygen \(= 5.6\) \(L\)
 
Molar volume of oxygen at STP \(= 22.4\) \(L\)
 
Formula:
 
The formula to find the number of moles from the volume is,
 
Numberofmoles=GivenvolumeofO2atSTPMolarvolumeatSTP
 
Solution:
 
By substituting the values in the above formula, we get,
 
Numberofmoles=5.622.4=0.25moles
 
Hence, the number of moles in \(5.6\) \(L\) of oxygen at STP\(=0.25\) \(moles\)
 
3Calculate the number of moles of a sample that contains \(12.046\times10^{23}\) atoms of iron.
 
Data:
 
Given the number of atoms of iron \(=12.046\times10^{23}\)
 
Avogadro's number \(=6.023\times10^{23}\)
 
Formula:
 
Numberofmoles=NumberofatomsofironAvogadronumber
 
Solution:
  
Numberofmoles=12.046×10236.023×1023=2
 
Hence, the number of moles of a sample that contains \(12.046\times10^{23}\) atoms of iron\(=2\) \(moles\)