Which represents the empirical formula for a3b9

The empirical formula  will be AB₃.

Explanation:

In chemistry the empirical formula is an expression that represents the simplest proportion in which the atoms that form a chemical compound are present. It is therefore the simplest representation of a compound.

In this example the compound A₃B₉ has 3 atoms of A and 9 atoms of B.

The simplest positive integer ratio of atoms of the compound will be 1:3 (1 atom of A and 3 atoms of B). In other words we have to divide by 3 each subindex of the compound.

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