The number of obligate categories which are always used in a taxonomic hierarchy are
(a) 7
(b) 5
(c) 3
(d) 8

Options

A. 7
B. 5
C. 3
D. 8

Answer

To solve the question regarding the number of obligate categories used in a taxonomic hierarchy, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Taxonomic Hierarchy**: Taxonomic hierarchy is a system used to classify and organize living organisms into categories based on their similarities and differences. It helps in understanding the diversity of organisms and identifying unknown organisms.

2. **Identify the Origin**: The taxonomic hierarchy was established by Carl Linnaeus in the 18th century. He introduced a systematic approach to classify organisms.

3. **List the Categories**: The main taxonomic categories (or ranks) in the hierarchy, in order from the broadest to the most specific, are:
- Kingdom
- Phylum (or Division for plants)
- Class
- Order
- Family
- Genus
- Species

4. **Count the Categories**: By counting the categories listed above, we find:
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
This totals to 7 categories.

5. **Select the Correct Answer**: Based on the count of the obligate categories in the taxonomic hierarchy, the answer to the question is (a) 7.

### Final Answer:
The number of obligate categories which are always used in a taxonomic hierarchy is **7** (Option a).

---