Answer
$B_5H_7$
Work Step by Step
Atomic weights (g/mol): $B: 10.81,\ H: 1.008$
In 100.0 g:
B: $88.5\ g \div 10.81= 8.19\ mol$
H: $11.5\ g\div 1.008 = 11.4\ mol$
Normalizing by the smallest amount of moles:
B: $8.19/8.19= 1.0$
H: $11.4/8.19=1.4$
To get integer numbers, we multiply each proportion by 5 which yields:
Empirical formula $B_5H_7$
