What is the formula of rust?

• A.  \[\text{F}{{\text{e}}_{\text{3}}}{{\text{O}}_{\text{4}}}\]                      
• B.  \[\text{F}{{\text{e}}_{\text{2}}}{{\text{O}}_{\text{3}}}\]
• C.  \[\text{FeO}\]                                    
• D. None of these