3.49g of ammonia at STP weighs 4.48litre calculate molecular mass of it.
4.48 l is not a weight. It is the volume occupied.
4.48 l at STP is 4.48/22.4 = 0.200 moles
1 mole would have a mass of 3.49*5 = 17.45 g
The correct molecular mass of NH3 is actually 17.02 g