The molar mass is 239g and therefore is 0.239 kg . Need to use kg or gram depends on the question . If 2 g of mass then the 2/239 if 0.2kg of mass then use 0.2/.239 to equate with N/Na.
Next: If Q is positive hence heat is absorbed by the system of gas. I dont know about the air bubble because it can either absorb or remove the heat . Both is possible.
Next: The induced emf = negative (rate of change of flux linkage) . Nothing wrong if forget the negative sign but it should be there,
So if current producing the flux is sine and differentiate is cosine , then add a negative sign . should result in negative cosine
