0.44 gram of a colorless oxide of nitrogen occurs 224 ml at stp. write the molecular formula of the compound

mols = 224/22,400 = ?

mols = grams/molar mass. You have mols and grams, solve for molar mass.
The rest of it is by trial and error.
molar mass = 44.
I would subtract 14 for one N which leaves 30 but 30 is not divisible by 16 evenly so NOx can't be right. Then I would try 2 N atoms.
That is 28 and 44-28 = 16 which is divisible by 16 evenly.