Thank you for posting your question!
When you have a molecular mass question like this it’s helpful to start by thinking of the sample as being 100 g, that way you can convert over from percentages to grams directly. So this sample would be 44.45 g C, 3.73 g H, and 51.82 g N.
The next step then is to convert the gram amounts over into moles using the molar mass for each of the elements. That information is commonly available either online or on the Periodic Table … looking it up I find that C is 12.01 g/mol, H is 1.01 g/mol, and N is 14.01 g/mol.
That means that after converting we would have
44.45 / 12.01 = 3.70 mol C
3.73 / 1.01 = 3.70 mol H
51.82 / 14.01 = 3.70 mol N
Those mole amounts being equal means that the ratio in the molecular formula between them is going to be 1:1:1.
Finally then to find the exact formula we want to figure out what the subscripts would be based on the molecular mass of 135.14 u.
That would be 135.14 / (12.01 + 1.01 + 14.01) = 5
Meaning that the ending molecular formula would be C₅H₅N₅
I hope that helps! You can use that same type of process whenever you are computing these :)
