The green colour solution of an Fe2+ salt changes to a brown solution of an Fe3+ salt by

 The green colour solution of an Fe2+ salt changes to a brown solution of an Fe3+ salt by

A. conversion.

B. elimination.

C. oxidation.

D. reduction

E. substitution

Explanation: 

In this question, a chemical reaction involving a change in oxidation state is involve. The green colour solution of an Fe2+ salt changes to a brown solution of an Fe3+ salt. This change in colour is a clue that a chemical reaction has occurred. But what kind of reaction is this? 

This is oxidation and reduction. Oxidation is the process where a substance loses electrons, and reduction is the process where a substance gains electrons. These reactions often occur together in what is call redox reactions commonly called oxidation-reduction reactions).

In this case, the Fe2+ ions is changing to Fe3+ ions. This means that each Fe2+ ion is losing one electron to become an Fe3+ ion. When an ion loses electrons, we say that it has been oxidized. Therefore, the correct answer is Option C: oxidation.

The other options given don't correctly express what is happening in this reaction. 

A conversion (Option A) is a general term that doesn't specific what type of reaction is occurring. 

Elimination (Option B) typically refers to a type of organic reaction where small molecules are removed from larger ones. 

Reduction reaction (Option D) is the opposite of oxidation - it's when a substance gains electrons, which is not what is happening here. 

Substitution (Option E) refers to a type of reaction where one atom or group of atoms is replaced by another.

SOURCE: NECO CHEMISTRY 2001 QUESTION 22