What is a functional group ? Write the functional groups of the following :
(i) Thioalcohol (ii) Isothiocyanate (iii) Thiocyanate and (iv) Sulphonic acid (v) Sulphones (vi) Sulphoxides.

Explanation

### Step-by-Step Solution:

1. **Definition of Functional Group:**
A functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. It determines the properties and reactivity of the compound.

2. **Functional Groups of the Given Compounds:**
- **(i) Thioalcohol:**
- Functional Group: Thio (-SH)
- Structure: R-SH (where R is an alkyl group)

- **(ii) Isothiocyanate:**
- Functional Group: Isothiocyanate (-N=C=S)
- Structure: R-N=C=S (where R is an alkyl group)

- **(iii) Thiocyanate:**
- Functional Group: Thiocyanate (-SCN)
- Structure: R-SC≡N (where R is an alkyl group)

- **(iv) Sulphonic Acid:**
- Functional Group: Sulphonic acid (-SO₃H)
- Structure: R-SO₃H (where R is an alkyl group)

- **(v) Sulphones:**
- Functional Group: Sulphone (-SO₂-)
- Structure: R-SO₂-R' (where R and R' are alkyl groups)

- **(vi) Sulphoxides:**
- Functional Group: Sulphoxide (-S=O)
- Structure: R-S(=O)-R' (where R and R' are alkyl groups)

### Summary of Functional Groups:
- Thioalcohol: -SH
- Isothiocyanate: -N=C=S
- Thiocyanate: -SCN
- Sulphonic Acid: -SO₃H
- Sulphones: -SO₂-
- Sulphoxides: -S=O