Aliphatic compounds are organic compounds that consist of straight or branched chains of carbon atoms. They are characterized by their ability to form covalent bonds with other atoms through sigma bonds. Aliphatic compounds include alkanes, alkenes, and alkynes.

Here is an explanation of why option 'A' is not associated with aliphatic compounds:

a) They contain (4n + 2) pi electrons:
This statement is not associated with aliphatic compounds. It is actually related to aromatic compounds. Aromatic compounds are cyclic compounds with a specific arrangement of atoms, known as an aromatic ring. They exhibit a special stability due to delocalized pi electrons. The number of pi electrons in an aromatic compound follows the rule (4n + 2), where 'n' is an integer. Aliphatic compounds, on the other hand, do not have aromatic rings and do not follow this rule.

b) They contain straight chain compounds:
This statement is true and associated with aliphatic compounds. Aliphatic compounds can have straight chains of carbon atoms. Alkanes, for example, are aliphatic compounds with a straight chain of carbon atoms and only single bonds.

c) They contain branched chain compounds:
This statement is also true and associated with aliphatic compounds. Aliphatic compounds can have branched chains of carbon atoms. Alkenes and alkynes, for example, are aliphatic compounds that can have branched chains.

d) They have an appropriate number of H-atoms and functional groups:
This statement is also true and associated with aliphatic compounds. Aliphatic compounds have an appropriate number of hydrogen (H) atoms and functional groups. The number of hydrogen atoms in aliphatic compounds is determined by the number of carbon atoms and the type of bonds present.

In summary, option 'A' is not associated with aliphatic compounds because it refers to the (4n + 2) pi electron rule, which is actually related to aromatic compounds. Aliphatic compounds do not have aromatic rings and do not follow this rule.