The functional group represent alcohol is:
A. ${\text{ - OH}}$
B. ${\text{ - CHO}}$
C. ${\text{ - COOH}}$
D. ${\text{RCOR}}$

Hint: Hydrocarbons are chemical compounds consisting entirely of carbon and hydrogen. They are a subset of organic compounds. They range from methane, which is just one carbon atom bonded to four hydrogen atoms, to polymers which consists of thousands of carbon and hydrogen atoms.

Complete step by step solution:
Functional group is an atom or a group of atoms within a molecule that is responsible for its characteristic chemical reactions. It often contains oxygen, nitrogen, sulfur or phosphorus. For an organic molecule. For an organic molecule to be reactive, it needs something additional. There are different types of functional groups-hydrocarbons, groups containing halogens, oxygen, nitrogen, sulfur, phosphorus, boron.
Saturated hydrocarbons are the simplest of the hydrocarbon species. They are composed entirely of single bonds and are saturated with hydrogen. Unsaturated hydrocarbons have one or more double or triple bonds between carbon atoms. Haloalkanes are compounds having halogens.
There are many compounds that contain ${\text{C - O}}$ bonds. They are alcohol, ketone, aldehyde, carboxylic acid, ester, ether.
Now let’s consider the given options.
A. The family of compounds that contain one or more hydroxyl groups attached to a single bonded alkane. It is represented by ${\text{R - OH}}$.
In option B, when ${\text{ - CHO}}$ is attached, then it is called aldehyde. In option C, when ${\text{ - COOH}}$ is attached to a carbon, it is called carboxylic acid. In option D, ${\text{RCOR}}$ is referred to as ketone group.

So, the correct option is A.

Note: In primary alcohols, carbon which carries the hydroxyl group is only attached to one alkyl group. In secondary alcohol, the carbon with the hydroxyl group attached is joined directly to two alkyl groups, which may be the same or different. In tertiary alcohols, carbon atoms holding the hydroxyl group are attached directly to three alkyl groups.