Question

Which of the following is a polyatomic ion?
A. \[Z{n^{2 + }}\]
B. \[PO_4^{3 - }\]
C. \[M{g^{2 + }}\]
D. \[C{r^{3 + }}\]

Answer 1

Hint: Poly means many or multiple, atomic means consisting of atoms and ions are nothing but atoms with charge. If we put these transliterations together, the meaning of the word is ions which consist of more than one atom in a single group.

Complete Step-by-Step Answer:
Let us now discuss the options given to us:
1. \[Z{n^{2 + }}\] : We can observe that the given ion is the +2-oxidation state of the element Zinc. The atomic number of zincs is 30 and hence its electronic configuration can be given as: \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^{10}}\] . Hence, when the ion of Zinc is being formed, it donates electrons from the 4s orbital to obtain that +2-oxidation state. Hence this ion of Zinc is a monatomic ion
2. \[PO_4^{3 - }\] : We can observe that this ion contains more than one type of atoms. This ion consists of phosphorus and oxygen. Because of this, this ion can be considered to be a polyatomic ion.
3. \[M{g^{2 + }}\] : We can observe that the given ion is the +2-oxidation state of the element Magnesium. The atomic number of Magnesium is 24 and hence its electronic configuration can be given as: \[1{s^2}2{s^2}2{p^6}3{s^2}\] . Hence, when the ion of Magnesium is being formed, it donates electrons from the 3s orbital to obtain that +2-oxidation state. Hence this ion of magnesium is a monatomic ion.
4. \[C{r^{3 + }}\] : We can observe that the given ion is the +3-oxidation state of the element Chromium. The atomic number of Chromium is 12 and hence its electronic configuration can be given as: \[1{s^2}2{s^2}2{p^6}3{s^2}3{p^6}4{s^2}3{d^4}\] . Hence, when the ion of Chromium is being formed, it donates electrons from the 4s orbital to obtain that +3-oxidation state. Hence this ion of Chromium is a monatomic ion.

Hence, Option B is the correct option

Note: Polyatomic ions contain more than one type of atom in the ion. The majority of polyatomic ions are anions that are named ending in -ate or -ite. Some anions have multiple forms and are named accordingly.