Question

what do you mean by functional group present in an organic compound . write the formula​

Answer 1

The functional group is defined as an atom or groupof atoms joined in a specific manner, which gives the chemical properties of the  organic compound and are the centers for chemical reactivity. ...

For example Thefunctional group presence in the alkene is -C=C- (double bond).

Answer 2

Heteroatoms confer specific properties to the compound, regardless of the length and nature of the long carbon chain and hence are called Functional Groups.

In a hydrocarbon chain, one or more hydrogens can be replaced by halogens, Oxygen, nitrogen and sulphur such that the valency of carbon remains satisfied. In such compounds, the element replacing hydrogen is referred as heteroatoms.

The above attachment tabulates some functional groups in carbon compounds.