Mendel published his work on inheritance of characters in 1865, but it remained unrecognised till 1900 due to the reason (s)
(A) Communication was not easy in those days.
(B) His contemporaries did not accept factors as discrete units of heredity.
(C) Mathematical approach to explain inheritance was totally new.
(D) Mendel could not provide any physical proof for the existence of factors

Options

A. Only A and B are correct
B. Only B and C are correct
C. Only C and D are correct
D. All are correct.

Answer

To answer the question regarding why Mendel's work on inheritance remained unrecognized until 1900, we can analyze the options provided:

1. **Communication was not easy in those days.**
- In the 19th century, scientific communication was limited. Mendel published his findings in a journal that was not widely circulated, which meant that many scientists were unaware of his work.

2. **His contemporaries did not accept factors as discrete units of heredity.**
- Mendel proposed the idea of "factors" (now known as genes) as discrete units of heredity. However, many scientists at the time were not ready to accept this concept, as the prevailing theories of inheritance were different.

3. **Mathematical approach to explain inheritance was totally new.**
- Mendel's use of mathematical and statistical methods to analyze inheritance patterns was innovative. At that time, the scientific community was not accustomed to applying such quantitative approaches to biological problems, which made it difficult for his work to be appreciated.

4. **Mendel could not provide any physical proof for the existence of factors.**
- During Mendel's time, the technology to visualize or prove the existence of genes (like microscopy) was not available. This lack of physical evidence made it challenging for others to accept his theories.

Based on the analysis of these options, it is clear that all of them contributed to the lack of recognition of Mendel's work until 1900.

### Final Answer:
All of the following reasons contributed to the unrecognized status of Mendel's work until 1900:
- (A) Communication was not easy in those days.
- (B) His contemporaries did not accept factors as discrete units of heredity.
- (C) Mathematical approach to explain inheritance was totally new.
- (D) Mendel could not provide any physical proof for the existence of factors.