What is the empirical formula of #B_3N_3H_6#?

The thing to remember about a compound's molecular formula is that it is always a multiple of its empirical formula.

That is the case because the empirical formula tells you the smallest whole number ratio that exists between a compound's constituent elements.

By comparison, the molecular formula tells you the exact number of atoms of each constituent element present in one molecule of said compound.

In your case, the molecular formula is said to be

#"B"_3"N"_3"H"_6 -># molecular formula

This tells you that one molecule of this compound contains

• three atoms of boron, #3 xx "B"#
• three atoms of nitrogen, #3 xx "N"#
• six atoms of hydrogen, #6 xx "H"#

Now, the smallest whole number ratio that exists between the elements is

#3 : 3 : 6 |div 3 implies 1:1:2#

This would make the compound's empirical formula

#"B"_1"N"_1"H"_2 implies color(green)(|bar(ul(color(white)(a/a)color(black)("BNH"_2)color(white)(a/a)|)))#

This means that you need three empirical formulas, #3 xx "BNH"_2#, to get the molecular formula for borazine, #"B"_3"N"_3"H"_6#.