a sample of ammonia weigh 3.00 g.what mass of sulphur trioxide contain the same number of molecules as are in 3.00g ammonia?

Molecular formula for ammonia is NH₃  whereas for sulphur trioxide is SO₃.
Number of moles = given mass/ Molar mass
given mass of ammonia= 3.0 g
​Molecular mass of NH₃ = 14+3
                                       = 17 g/mol
No. of moles = 3/17
                    =0.176 mol
​Molecular mass of sulphur trioxide = 32+16$\times$3
                                                        = 80 g/mol
Number of moles of sulphur trioxide = Number of moles of ammonia = 0.176 mol
Mass of sulphur trioxide having 0.176 mol = 0.176$\times$80
                                                                   =14.08 g

​Hence 14.08 g sulphur trioxide has same number of molecules as 3.0 g of ammonia.