Mendel published his work on inheritance of characters in 1865 butit remained unrecognised till 1900 because
(a) He could not provide any physical proof for the existance of factors
(b) His concept of factors as stable, discrete units that acceptance from the contemporaries
(c ) Mendel's approach of using approach of using mathematics to explain biological phenomena was totally old
(d) Communication was not easy (as it is now)

Options

A. (a), (b) & (c ) are correct
B. (c ) & (d) are correct
C. (a), (b) & (d) are correct
D. Only (a) is correct

Answer

To answer the question regarding why Mendel's work on inheritance remained unrecognized until 1900, we can analyze each of the provided options step by step.

### Step-by-Step Solution:

1. **Understanding Mendel's Work**: Mendel published his findings on the inheritance of traits in pea plants in 1865. His work laid the foundation for the field of genetics, but it was largely ignored for several decades.

2. **Analyzing Option (a)**:
- Mendel could not provide any physical proof for the existence of factors (alleles). At the time, microscopy had not advanced enough to visualize chromosomes and their behavior during cell division. This lack of physical evidence made it difficult for contemporaries to accept his theories.
- **Conclusion**: This statement is true.

3. **Analyzing Option (b)**:
- Mendel proposed that factors (now known as genes) are stable, discrete units that exist in pairs. However, this concept was not widely accepted by his contemporaries because they lacked the understanding of genetics and the physical basis of heredity.
- **Conclusion**: This statement is also true.

4. **Analyzing Option (c)**:
- The statement claims that Mendel's use of mathematics to explain biological phenomena was totally old. In fact, Mendel's approach was innovative and ahead of its time, as he applied statistical methods to biological data, which was not common practice at that time.
- **Conclusion**: This statement is false.

5. **Analyzing Option (d)**:
- Communication in the 19th century was not as efficient as it is today. Scientific journals had limited circulation, and Mendel's work was published in a relatively obscure journal that did not reach a wide audience. This contributed to the lack of recognition of his findings.
- **Conclusion**: This statement is true.

6. **Final Evaluation**:
- Based on the analysis, options (a), (b), and (d) are correct reasons for the unrecognized status of Mendel's work until 1900. Option (c) is incorrect.

### Answer:
The correct options are (a), (b), and (d).