Question

In which of the following oxoanions the oxidation state of the central atom is not same as that of its group number in the periodic table.
A. $Mn{{O}_{4}}^{-}$
B. $C{{r}_{2}}{{O}_{7}}^{2-}$
C. $V{{O}_{4}}^{3-}$
D. $Fe{{O}_{4}}^{2-}$

Answer 1

Hint: Oxoanion can also be known by the name oxyanion which are generally represented by the molecular formula ${{A}_{x}}{{O}_{y}}^{Z-}$ where A represents chemical element, O represents oxygen and z represents the charge carried by the anion. Charge shown is always negative as anion is those compounds which contain negative charge.

Complete Step by step solution: The oxidation state of an atom can be defined as the hypothetical charge that would be held by that atom if all of its bonds to other atoms were completely ionic in nature Hence to find the answer we have to calculate the oxidation state of the elements present in them. We know that the oxidation state of oxygen atoms is -2.
A. $Mn{{O}_{4}}^{-}$ in this case oxidation state of Mn is calculated by supposing it x and x can be calculated as: $x+(-2\times 4)=-1;x=-1+8=7$ and we know that Mn belongs to group 7.
B. $C{{r}_{2}}{{O}_{7}}^{2-}$ similarly assume oxidation state of Cr is x and x is given as:
$2x+(-2\times 7)=-2;2x=-2+14;x=6$, Cr also belongs to group 6.
C. $V{{O}_{4}}^{3-}$x is given as: $x+(4\times -2)=-3;x=-3+8;x=5$, Vanadium belong to group 5.
D. $Fe{{O}_{4}}^{2-}$ in this case x is given by: $x+(4\times -2)=-2;x=-2+8;x=6$ but we know that iron belongs to group 8 so this is not as same as central atom.

Hence we can say that option D is the correct answer.

Note: Oxidation state can also be explained in some easy manner i.e. it generally gives us information about the number of electrons lost by an atom which further describes the extent of oxidation of the atom. Oxidation state of an atom may be zero, negative or positive.