solution:
First we calculate the number of mole of gas as follows: 
PV = n RT 
Here temperature; T= 100°C or 373 K 
n = PV/ RT 
= 4.78 atm * 3.82 L / 0.0821 L ∙ atm / mol ∙ K * 373 K 
= 0.596 Moles 
Now determine the molar mass of gas as follows: 
Number of moles = amount in g/ molar mass 
Molar mass = 19.08 grams / 0.596 Moles 
= 32.013 g/ mole 
This the molar mass of O2 hence the gas is oxygen