Which is the correct formula for phosphate ion?

Which is the correct formula for phosphate ion?

• A. NO3-
• B. CO3^2-
• C. PO4^3-
• D. SO4^2-

Answer: (C)

Phosphate is an oxoan ion with a phosphorus atom bonded to four oxygen atoms and it carries a total charge of -3. This combination is written as PO4 with a 3− charge, or PO4^3−. The four oxygens and the -3 charge come from the way the negative charge is distributed across the oxygens in resonance, giving a tetrahedral arrangement around phosphorus. Other common anions differ in either the number of oxygens or the overall charge: nitrate has three oxygens and a -1 charge (NO3−), carbonate has three oxygens and a -2 charge (CO3^2−), and sulfate has four oxygens but a -2 charge (SO4^2−). The four-oxygen, -3 charge combination uniquely corresponds to phosphate, so PO4^3− is the correct formula.

Phosphate is an oxoan ion with a phosphorus atom bonded to four oxygen atoms and it carries a total charge of -3. This combination is written as PO4 with a 3− charge, or PO4^3−. The four oxygens and the -3 charge come from the way the negative charge is distributed across the oxygens in resonance, giving a tetrahedral arrangement around phosphorus.

Other common anions differ in either the number of oxygens or the overall charge: nitrate has three oxygens and a -1 charge (NO3−), carbonate has three oxygens and a -2 charge (CO3^2−), and sulfate has four oxygens but a -2 charge (SO4^2−). The four-oxygen, -3 charge combination uniquely corresponds to phosphate, so PO4^3− is the correct formula.