Answer: The molecular formula will be 
Explanation:
If percentage are given then we are taking total mass is 100 grams.
So, the mass of each element is equal to the percentage given.
Mass of H = 5.80 g
Mass of N = 20.16 g
Mass of O = 23.02 g
Mass of Cl = 51.02 g
Step 1 : convert given masses into moles.
Moles of H =
Moles of N =
Moles of O =
Moles of Cl =
Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.
For H = 
For N =
For O = 
For Cl =
The ratio of H: N: O: Cl= 4: 1: 1: 1
Hence the empirical formula is
The empirical weight of
= 4(1)+1(14)+ 1(16) + 1(35.5)= 69.5 g.
The molecular weight = 278 g/mole
Now we have to calculate the molecular formula.
The molecular formula will be=