Which of the following ions has a -1 charge?

Cyanide carries a -1 charge because it consists of a carbon atom triple-bonded to a nitrogen atom. In this ion, the carbon has a formal charge of 0, while the nitrogen has a formal charge of -1, resulting in an overall charge of -1 for the ion.

The sulfate ion (SO4) typically carries a -2 charge; it consists of one sulfur atom surrounded by four oxygen atoms, and the overall bonding and oxidation states lead to this charge.

Oxalate (C2O4) is also a -2 charged ion. It contains two carbon atoms and has a structure that results in this higher negative charge due to the combination of bonds with oxygen atoms.

Nitrate (NO3) has a -1 charge, similar to cyanide, but its structure and charge assignment come from a different arrangement of nitrogen and oxygen. However, in this question, cyanide is specifically mentioned as the ion with the -1 charge, making it the appropriate choice.