In the following structure, carbons (I),(2),(3) and (4) are classified respectively as

Carbon (i) : quaternary carbon

Carbon (ii) : secondary carbon

Carbon (iii) : tertiary carbon

Carbon (iv) : secondary carbon

Explanation:

Carbons can be classified into 4 categories:

(1) Primary carbon : These are the atoms where the carbon atom is attached to one other carbon atom.

(2) Secondary carbon : These are the atoms where the carbon atom is attached to two other carbon atoms.

(3) Tertiary carbon : These are the atoms where the carbon atom is attached to three other carbon atoms.

(4) Quaternary carbon : These are the atoms where the carbon atom is attached to four other carbon atoms.

In the given structure:

Carbon (i) is attached to 4 further carbon atoms and hence, it is a quaternary carbon.

Carbon (ii) is attached to 2 further carbon atoms and hence, it is a secondary carbon.

Carbon (iii) is attached to 3 further carbon atoms and hence, it is a tertiary carbon.

Carbon (iv) is attached to 2 further carbon atoms and hence, it is a secondary carbon.