I can't tell if the "Tl" is a capital T and lowercase L, or if it is a capital i. If it is a lowercase L, it is an element. But if it it is a capital i, then it is a compound. The way I know if it is a compound or element is because if there is only one capital letter, it indicates that only one element is present, therefore making it an element. Although if there is more than one capital letter, it must be a compound because two elements are chemically put together, creating a compound.