An order can be best defined as :-

Options

A. A group of related species and genera of different taxa
B. A group of related families which exhibit a few similar characters
C. A group of related classes which exhibit a few similarites
D. An assemblage of genera related to different classes

Answer

To answer the question "An order can be best defined as:", we will analyze the options provided and determine the correct definition of an order in the context of biological classification.

### Step-by-Step Solution:

1. **Understanding Biological Classification**:
- Biological classification is a hierarchical system used to organize living organisms into groups based on shared characteristics. The main ranks in this hierarchy include kingdom, phylum, class, order, family, genus, and species.

2. **Analyzing the Options**:
- **Option A**: A group of related species and genera of different taxa.
- This option mixes different taxonomic ranks and does not accurately define an order.
- **Option B**: A group of related families which exhibit a few similar characters.
- This option correctly identifies that an order is composed of related families that share certain characteristics.
- **Option C**: A group of related classes which exhibit a few similarities.
- This option is incorrect because an order is not made up of classes; it is a rank below class.
- **Option D**: An assemblage of genera related to different classes.
- This option is also incorrect as it suggests a mix of different classes, which does not define an order.

3. **Conclusion**:
- After analyzing all the options, **Option B** is the best definition of an order. An order is indeed a group of related families that exhibit a few similar characters.

### Final Answer:
**An order can be best defined as: b. A group of related families which exhibit a few similar characters.**

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