Assertion: Eukaryotic cells show extensive compartmentalisation of cytoplasm.
Reason: The presence of membrane - bound organelles is an important character in eukaryotes:
A: Both (A) and (R) are true and reason is the correct explanation of (A).
B: Both (A) and (R) are true but reason is not the correct explanation of (A).
C: (A) is true but the (R) is false.
D: (A) is false but (R) is true

Hint: Eukaryotic cells are huge and complex organisms having a nucleus encased within the nuclear membrane. Eukaryotic cells can be found in protozoa, fungi, plants, and animals. Eukaryota is the kingdom in which they are categorised. They have the ability to maintain many habitats in a single cell, allowing them to carry out a variety of metabolic operations. This allows them to grow hundreds of times larger than prokaryotic cells. Unicellular or multicellular eukaryotic cells exist.

Complete answer:
Option A: The presence of membrane bound organelles in eukaryotic cells allows for substantial cytoplasm compartmentalization. Eukaryotic cells have a nuclear envelope and a well-organized nucleus.
So, option A is incorrect.
Option B: The cytoplasm of eukaryotes is highly compartmentalised. In cell biology, cellular compartments are all of the closed regions of a eukaryotic cell's cytoplasm that are normally bordered by a single or double lipid layer membrane. The process of forming cellular compartments is referred to as compartmentalization. Endoplasmic reticulum, Golgi apparatus, nucleus, mitochondria, lysosomes, and other membrane-bound organelles are found in eukaryotes.
So, option B is correct.
Option C: The nucleus of eukaryotic cells is membrane-bound. In eukaryotic cells, the presence of membrane-bound organelles allows for significant cytoplasm compartmentalization.
So, option C is incorrect.
Option D: Eukaryotic cytoplasm is highly compartmentalised. Eukaryotes have an endoplasmic reticulum, a Golgi apparatus, a nucleus, mitochondria, lysosomes, and other membrane-bound organelles.
So, option D is incorrect.

Therefore, Option B is the correct answer.

Note:
Eukaryotic cells have the following characteristics:
The nucleus of eukaryotic cells is surrounded by the nuclear membrane and mitochondria. A eukaryotic cell's locomotory organs are flagella and cilia. The cell wall is the eukaryotic cell's outermost layer. A cytoskeletal structure is seen in eukaryotic cells. The nucleus has a single, linear DNA strand that holds all of the genetic information. Plants, mammals, fungi, protozoa, and other complex animals all have eukaryotic cells.