Question

The oxidation state of phosphorus varies from:
(A) $- 1$ to $+ 1$
(B) $- 3$ to $+ 3$
(C) $- 3$ to $+ 5$
(D) $- 5$ to $+ 1$

Answer 1

As we know that phosphorus belongs to group fifteen elements and it possesses a total of five electrons in its outermost valence shell so it needs three more electrons to attain the stable noble gas configuration after completing their octet or they can lose these electrons to become stable.

Complete Step by step answer: As we know that oxidation state is a property of an element where it shows how many electrons can an atom gain or lose to pair up with other atoms. Also we know that phosphorus belongs to group fifteen elements and we also know that group fifteen elements have an electronic configuration as $n{s^2}n{p^3}$ that suggests the outermost valence electrons of this group elements is $5$. Oxidation states of these elements is commonly $- 3, + 3$ and $+ 5$.
We are also aware that during moving down the group the size of atoms increases. Nitrogen shows three oxidation states which are $+ 1, + 2, + 4$.
Now comes the phosphorus which also shows the $+ 1$ and $+ 4$ oxidation state in some oxoacids. All intermediate oxidation states disproportionate into both acid and alkali into $- 3$ and $+ 5$. Since phosphorus have the five electrons in its valence shell so it has the tendency to gain three more electrons and thus shows an oxidation state of $- 3$ or they can lose five electrons to become more stable and thus show an oxidation state of $+ 5$. Thus phosphorus can show oxidation states between $- 3$ to $+ 5$.

Therefore the correct answer is (C).

Note: Tendency of showing $- 3$ oxidation state decreases down the group because of the increase in size and metallic characters. The stability of $+ 5$ oxidation state decreases and that of $+ 3$ oxidation state increases down the group and the reason for that trend is because of the inert pair effect. Phosphorus shows $- 3$ oxidation state with active metals as it is more electronegative than most of the metals and $- 3$ and $+ 5$ oxidation state with more electronegative non-metals.