At 22 degrees Celsius and a pressure of 755 mm Hg, an unknown gas was found to have a density of 4.52 g/L. When analyzed, the gas was found to consist of two elements: Boron at 78.1% and Hydrogen at 21.9%.

Question

At 22 degrees Celsius and a pressure of 755 mm Hg, an unknown gas was found to have a density of 4.52 g/L.  When analyzed, the gas was found to consist of two elements:  Boron at 78.1% and Hydrogen at 21.9%.
What is the molecular formula of this unknown gas?