To determine the chemical formula we will do a quick search of the compound's name in Pubchem. Source: https://pubchem.ncbi.nlm.nih.gov/
As this is a very prestigious and reliable source of information.
Our search returns the following results:
Hydroxide: OH⁻
Chromate: CrO₄⁻²
Phosphate: O₄P⁻³
Cyanide: CN⁻
