Arrange following functional group in the increasing order of priority of functional group:

The correct option is 1 > 4 > 3 > 2 > 6 > 5.

To determine the correct priority order of the functional groups, we refer to the standard IUPAC nomenclature rules for selecting the principal functional group. The priority order of the relevant functional groups in decreasing order is given as:

Carboxylic acid (−COOH) > Acid amide (−CONH₂) > Nitrile (−CN) > Aldehyde (−CHO) > Ketone (−CO−) > Amine (−NH₂)

Based on the provided image, we can analyze the priority relation between the specific groups shown:
−CONH₂ > −CN > −CHO > −CO > −NH₂

By mapping the numbered functional groups to their priority levels:
1 represents Carboxylic acid (−COOH)
4 represents Amide (−CONH₂)
3 represents Nitrile (−CN)
2 represents Aldehyde (−CHO)
6 represents Ketone (−CO−)
5 represents Amine (−NH₂)

Therefore, arranging them in the decreasing order of priority (indicated by the > sign in the options) yields:
1 > 4 > 3 > 2 > 6 > 5