Question

$2Mg+{{O}_{2}}\to 2MgO$
The above reaction is an example of:
(A) decomposition reaction
(B) displacement reaction
(C) combination reaction
(D) oxidation reaction

Answer 1

Hint: Think about the changes taking place during reaction. Write the definitions of each of the terms given in the question. Identify in which of the given options, the reaction fits properly and accordingly come to a conclusion.

Complete step by step answer:
- Let’s take a look at the reaction, $2Mg+{{O}_{2}}\to 2MgO$
- Magnesium metal reacts with oxygen to form magnesium oxide. This reaction takes place when magnesium metal is burnt in air.
- Oxygen and magnesium combine with each other to form magnesium oxide which is a white powder.
- Let’s look at the terms given in the options.

- Decomposition reaction is a reaction in which one reactant is disintegrated to form two or more
products. For example, calcium carbonate on heating decomposes to form calcium oxide and carbon dioxide.

- Displacement reaction is a reaction in which two reactants react with each other to form two products. A displacement reaction is the reaction wherein an atom or a set of atoms is/are displaced by another atom in a molecule. For example, zinc reacts with copper sulphate to form zinc sulphate and copper.

- Combination reaction is a reaction in which two reactants combine to form one product. For example, magnesium reacts with oxygen to form magnesium oxide.

- Oxidation reaction is the reaction in which there is addition of oxygen or removal of hydrogen. For example, magnesium reacts with air to form magnesium oxide.
- Therefore, the given reaction $2Mg+{{O}_{2}}\to 2MgO$ is an example of combination as well as oxidation reaction.
So, the correct answer is “Option C and D”.

Note: Remember the important concepts and one example for each type of reaction. This will help in answering these kinds of questions. Magnesium is an alkali metal and metals are electropositive in nature. Magnesium is also very reactive and will readily react with oxygen to form magnesium oxide.