Question

Homologue of $HCHO$ is:
A. $C{H_2}O$
B. $C{H_4}O$
C. ${C_2}{H_2}O$
D. ${C_2}{H_4}O$

Answer 1

We need to understand the concept of homologous series. A homologous series is a series of compounds with the same general formula but adding a single parameter gives the next compound of the series. An example of a homologous series is that of alkanes where adding a $- C{H_2}$ group gives the next alkane of the series and the compound which is produced by the addition or removal of this $- C{H_2}$ group is called a homologue. We can now study the homologue of the given compound.

Complete step by step answer:
We know that a homologous series is a series of compounds with the same general formula but adding a single parameter gives the next compound of the series or by removing the same parameter gives the previous homologue.
We must need to know that one molecule of $HCHO$ consists of one carbon atom, two hydrogen atoms and one oxygen atom. Its homologue is likely to carry an extra $- C{H_2}$ group. Hence one molecule of $HCHO$ will consist of two carbon atoms, four hydrogen atoms and one oxygen atom in its homologue. This addition is not applicable to the functional group present in the compound. Hence the formula of the homologue will be ${C_2}{H_4}O$ .

So, the correct answer is Option D.

Note: It must be noted that $HCHO$ is formaldehyde which is the simplest aldehyde it cannot have a homologue by removing the $- C{H_2}$ group. Since it contains only one carbon, it is obvious that a $- C{H_2}$ group must be added. A homologous series is a sequence of compounds with the same functional group and similar chemical properties in which the members of the series can be branched or unbranched, or differ by $- C{H_2}$ .Also the homologue of formaldehyde is ${C_2}{H_4}O$ which is acetaldehyde.