Biological concept of species proposed by :-

Options

A. Linnaeus
B. Mayr
C. John Ray
D. De Candolle

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks who proposed the biological concept of species. This concept is crucial in biology as it defines how species are classified based on their ability to interbreed.

2. **Identifying the Options**: The options provided are:
- A) Linnaeus
- B) Mayer
- C) John Ray
- D) D. Candole

3. **Analyzing Each Option**:
- **Linnaeus**: Known as the father of taxonomy, he introduced the binomial nomenclature system and classified organisms into two kingdoms but did not propose the biological concept of species.
- **Mayer**: He is credited with the biological species concept, which defines species based on their ability to interbreed and produce fertile offspring. This concept emphasizes reproductive isolation.
- **John Ray**: Proposed a typological species concept, which is different from the biological concept.
- **D. Candole**: Developed the Uniform Botanical Nomenclature and proposed rules for naming plants but did not propose the biological concept of species.

4. **Conclusion**: Based on the analysis, Mayer is the correct answer as he proposed the biological concept of species.

5. **Final Answer**: The biological concept of species was proposed by **Mayer** (Option B).