MgCO3?nH2O n=1～5, the remaining mass of the analysis image at 400℃ is 82.3g, which is the process of losing crystal water, that is, the mass of magnesium carbonate. The amount of 82.3g of magnesium carbonate is : 82.3g84g/mol=0.98mol, and the mass of 0.98mol magnesium oxide is 39.2g, so the remaining mass of 39.2g is the mass of carbon dioxide lost when magnesium carbonate decomposes, and 100g×18n18n 84=100-82.3 is obtained.
n=1,
So the answer is: 1.