Which of the following hydrocarbons undergo addition reactions?
${C_2}{H_6},{C_3}{H_8},{C_3}{H_6},{C_2}{H_2}{\text{ and C}}{{\text{H}}_4}$

Hint: The hydrocarbon compounds that have a carbon-carbon double bond or carbon-carbon triple bonds in their structure can undergo addition reactions. Alkanes cannot give addition reactions.

Complete step by step solution:
We will first what are addition reactions and then we will see which hydrocarbons can give this type of reactions.
- Addition reactions are the reactions in which the reactant molecule is added to the substrate molecule. So, only one product is formed upon reaction of two or more molecules.
- So, generally, the hydrocarbons which have C-C double bond or C-C triple bond can give these types of reactions.
- We will check which of the given molecules have carbon-carbon double bond or triple bond.
- We know that alkane has C-C single bonds. Alkene has a C-C double bond. Alkyne has a C-C triple bond. We can find the type of hydrocarbon from its molecular formula which can be given as under.
Alkane : ${C_n}{H_{2n + 2}}$
Alkene : ${C_n}{H_{2n}}$
Alkyne : ${C_n}{H_{2n - 2}}$
- So, from these formulae, we can say that ${C_2}{H_6}$ is an alkane because n = 2 and 2n+2 = 6
- ${C_3}{H_8}$ is also an alkane because n = 3 and 2n+2 = 8 Alkanes cannot undergo addition reactions.
- ${C_3}{H_6}$ is an alkene because n = 3 and 2n = 6. Thus, it will have a carbon-carbon double bond which can undergo addition reactions.
- ${C_2}{H_2}$ is an alkyne because n = 2 and 2n-2 = 2. So, this compound can also undergo addition reactions.
- $C{H_4}$ is an alkane because n = 1 and 2n+2 = 4. So, it only has C-C single bonds. Thus, it cannot undergo addition reactions.

Thus, we can conclude that only ${C_2}{H_6}{\text{ and }}{{\text{C}}_2}{H_2}$ can undergo addition reactions.

Note: Remember that the alkyne can give an addition reaction to form alkene. This alkene can also give an addition reaction to give alkane as the final product. Addition reactions differ from substitution reactions as there is a substitution of an atom or a group of atoms is there in substitution reactions