To determine the formula units of the given compound, we need to convert from grams to moles first then convert it to formula units by using the Avogadro's number. We do as follows:
23.5 g Sb2S3 ( 1 mol / 339.7 g ) ( 6.022 x 10^23 formula units / mol ) = 4.17x10^22 formula units Sb2S3