Simplify the following text for a Grade 9 native English-speaking person.
Original: The thallium ( III ) oxide is a black solid which decomposes above 800 Â C , forming the thallium ( I ) oxide and oxygen .
Simplified: The black oxide , thallium ( III ) oxide and the hydroxide , thallium ( III ) hydroxide , are the only stable +3 compounds . They break down to oxygen and thallium ( I ) oxide when heated .