Question

What does the empirical formula indicate?

Answer 1

Empirical formulas provide the lowest whole number ratio of elements present in a compound.

Formulas for ionic compounds are always empirical formulas.

Examples:
NaCl is a 1:1 ratio of sodium and chloride ions
`CaF_2` is a 1:2 ratio of calcium and fluoride ions
`Al_2O_3` is a 2:3 ratio of aluminum and oxide ions

Empirical fomulas also can be written for molecular compounds (covalent Bonding)

Examples:
Hydrogen peroxide (`H_2O_2`) has an empirical formula of `HO`.
Glucose (`C_6H_12O_6`) has an empirical formula of `CH_2O`.
Sucrose (`C_12H_22O_11`) has the same empirical formula as its molecular formula

Here is a video which discusses how to calculate an empirical formula.

Simple explanation, nice looking website https://www.chem.wisc.edu/deptfiles/genchem/sstutorial/Text6/Tx65/tx65.html