Question

Find the oxidation number of Magnesium in Magnesium Chloride:
(A) +1
(B) -1
(C) +2
(D) -2

Answer 1

Hint: Solve this question by summing the oxidation number of each element to 0 since this element has a net charge equal to zero. Assign a random variable ‘x’ for calculating oxidation number of Mg.

Complete step by step answer:

The compound Magnesium Chloride has the chemical formula - $MgC{{l}_{2}}$. As we can see it is a neutral compound, therefore its net charge = 0.
We can calculate the oxidation number of Magnesium by following methods.

1. Method 1 –
   Chlorine is a group 17 element and needs only one electron to complete its octet. So, its oxidation number is -1.
   Let the oxidation number of Magnesium be ‘x’.
   Therefore, (x) + 2(-1) = 0
   x = +2.
2. Method 2 –
   Magnesium is a group 2 element with atomic number 12.
   Its electronic configuration is $[Ne]3{{s}^{2}}$.
   As we can see, it can lose two electrons to gain the electronic configuration of Neon.
   Therefore, its oxidation number will be +2. Therefore option (C) +2 is the correct answer.

Additional Information: The oxidation number of an atom or element is a number that indicates the total number of electrons lost or gained by it.

Note: There are certain rules for calculating oxidation number –
- Oxidation number of any free element is zero.
- Oxidation number for a monatomic ion is equal to the net charge on it.
- Hydrogen, in general, has an oxidation state equal to +1. However, it is -1 in forms of a compound with an element with lesser electronegativity.
- Alkali metals have oxidation number = +1
- Alkali earth metals have oxidation number = +2
- Halogens have oxidation number = -1
- Oxygen has an oxidation number = -2, but in case of peroxides, it is -1.