Question

Bromine is converted to bromate ion. The oxidation number of bromine changes to _____.
A.0 to +1
B.0 to +3
C.0 to +5
D.0 to +7

Answer 1

Hint: To solve this question, we should have prior knowledge about the calculation of oxidation state and the definition of oxidation state. Oxidation state of an atom is defined as the number of electrons which are lost during a chemical reaction.

Complete answer:
The most frequent terms that are oxidation state and oxidation number are terms frequently used and interchangeable. They are defined and described as the number of electrons lost in an atom.
The chemical reaction involved when bromine is converted to bromate ion is mentioned below:
$$B{r}_2\to Br{O_3}^{-}$$
Oxidation number of bromine in the left hand side of the reaction is 0 because bromine is present in its standard form. And the oxidation number of bromine in the right hand side of the reaction will be:
Oxidation state of oxygen = -2
So, the oxidation state of bromine will be:
$$\begin{array}{rl}& x+3(-2)=-1\\ & x=-1+6\\ & x=+5\end{array}$$

Hence, the correct answer is option (C) i.e. Bromine is converted to bromate ion. The oxidation number of bromine changes 0 to +5.

Additional information:
Oxidation number is positive for halogens like chlorine, iodine. The sum of oxidation numbers added for different atoms in a compound should be equal to zero.

Note:
In most of the compounds the oxidation number of oxygen is -2 but this is not always correct. There are some exceptions to this. For example, when oxygen is bonded to fluorine at that time the oxidation number oxygen is equal to +1.