The first answer choice is correct: SF6 is a compound: it is a substance composed of more than one atom from different elements (sulfur and fluorine).
The second answer choice is incorrect: while SF6 is indeed a compound that contains seven atoms, those atoms are not identical since one is a sulfur atom and six are fluoride atoms.
The third answer choice is incorrect: SF6 is not an element because it can be separated chemically into simpler substances that are elements. All the atoms comprising an element must have the same number of protons (the same atomic number); sulfur and fluorine have different atomic numbers. There is no single nucleus in SF6; the S and six F atoms each has their own nucleus.
The fourth answer choice is incorrect; SF6 contains no carbon atom, and so wouldn’t meet a central criterion for an organic compound. Moreover, the formula SF6 indicates that the sulfur atom is not bonded to any other atom apart from fluorine atoms, and there are no bonding electrons left on the S. There is no plausible reason to think that a molecule with such weak intermolecular attractions as SF6 would form long chains of S atoms. Indeed, in standard conditions, SF6 is a gas.
