Question

Oxidation number of calcium in calcium phosphate:
\[
  A{.1^ + } \\
  B{.1^ - } \\
  C.0 \\
  D{.2^ + } \\
  E{.3^ + } \\
\]

Answer 1

Hint: In order to solve this problem we need to know that the number of electrons needed to share to make the bonds. Then we have to determine the element gains or lost the electron then according to that we have to determine the oxidation number. Knowing this will solve your problem and will give you the right answer.

Complete step-by-step answer:
As we know that the electro - valency of alkaline earth metals are always +2. So, the oxidation state of Ca is also +2.
Oxygen has -2 oxidation in most of its compounds. In the case of peroxides, however, the oxidation number corresponding to oxygen is -1. All alkali metals (group 1 elements) have a +1 oxidation state in their compounds. Both alkaline earth metals (group 2 elements) exhibit a +2 oxidation state in their compounds. For compounds composed of two elements, the halogen (group 17 elements) has an oxidation number of -1 assigned to them. In the case of neutral compounds, the sum of all oxidation numbers of the constituent atoms is zero. When polyatomic ions are considered, the sum of all the oxidation numbers of the atoms that form them is equal to the net charge of the polyatomic ion. The oxidation number of an atom in a given compound can therefore be calculated using the steps mentioned above.

The formula of calcium phosphate is $C{a_3}{(P{O_4})_2}$. As the charge of phosphate ion ${(P{O_4})^{ - 3}}$ is -2.
And as we see that the molecule as a whole is neutral, so to neutralize the molecule we need to know that the charge on calcium is +2.
Then the charge +6 and -6 on calcium and phosphate will cancel out each other. And will give you the molecule calcium phosphate.
Hence, the correct answer is +2.
So, the correct option is D.

Note – When you get to solve such problems you need to know the various methods to find oxidation numbers. There are various methods to find the oxidation number of an element as well as the molecule. Each free product has an oxidation value equal to zero. In the case of monatomic ions, the oxidation number also has the same value as the net charge corresponding to the molecule. Hydrogen atom (H) has an oxidation state of +1. Nevertheless, when bound to an element with less electronegativity than that, the oxidation number is -1.