Introduction:
In the Whittaker system, organisms are classified into five kingdoms based on their mode of nutrition, cellular organization, and other characteristics. These kingdoms include Monera, Protista, Fungi, Plantae, and Animalia. To determine the number of kingdoms a multicellular eukaryotic organism with a holophytic mode of nutrition belongs to, we need to consider its characteristics and identify the appropriate kingdom(s) it fits into.

Holophytic Mode of Nutrition:
Holophytic nutrition, also known as autotrophic nutrition, is a mode of nutrition where organisms synthesize their own food using inorganic substances such as water, carbon dioxide, and sunlight. In this process, known as photosynthesis, organisms convert light energy into chemical energy to produce glucose and oxygen. This mode of nutrition is primarily observed in plants, algae, and some bacteria.

Classification:
Based on the characteristics mentioned, let's analyze the possible kingdoms to which a multicellular eukaryotic organism with holophytic nutrition can belong:

Kingdom Plantae:
Plants are multicellular eukaryotic organisms that possess chloroplasts and conduct photosynthesis to synthesize their own food. They have a well-developed structure, including roots, stems, and leaves. Examples of plants include trees, shrubs, herbs, and mosses.

Kingdom Protista:
Protists are eukaryotic organisms that exhibit a wide range of characteristics and modes of nutrition. Some protists, such as algae, are capable of photosynthesis and have a holophytic mode of nutrition. They can be unicellular or multicellular, and examples include diatoms, green algae, and brown algae.

Conclusion:
A multicellular eukaryotic organism with a holophytic mode of nutrition can belong to two kingdoms in the Whittaker system: Plantae and Protista. The kingdom Plantae includes well-developed and differentiated plants, while the kingdom Protista encompasses diverse eukaryotic organisms, including photosynthetic protists such as algae. The specific classification of the organism would depend on its characteristics and further taxonomic analysis.

1 i.e. kingdom plantae