Five kingdom system of classification suggested by R.H. Whittaker is not based on:

The correct option is A Presence or absence of a well-defined nucleus
Five kingdom classification puts unicellular and multicellular organisms into different groups.

The main principle for analysis by R.H. Whittaker include:
1. Complexity of cell structure (eukaryotic or prokaryotic)
2. Body organization (unicellular or multicellular)
3. Thallus organization
4. Mode of nutrition (autotrophs or heterotrophs)
5. Reproduction (sexual or asexual)
6. Phylogenetic relationships

Therefore, presence or absence of a well-defined nucleus is not the basis for R.H. Whittaker's classification.