If a 0.050g sample of the boron hydride burns completely in #O_2#, what will be the pressure of the gaseous water In a 4.25-L flask at 30.0°C?
I assume that you mean diborane,
You are presumed to have
By the stoichiometry of the reaction listed, for each mole of diborane that combusts,
Why did I use
Please note that this answer rests on the assumption that you mean diborane. There are many other borohydrides.