X = ..................... identified DNA as an acidic substance present in the nucleus of a cell. He named it as Y = ..........

Options

A. X = Avery, Y = Negatoid.
B. X = Stein, Y = DNA Nucleolus.
C. X = William Harvey, Y = Nucleoid
D. X = Friedrich Meischer Y = Nuclein

Explanation

To solve the question, we need to identify the scientist who first recognized DNA as an acidic substance present in the nucleus of a cell and the name he gave to it.

### Step-by-Step Solution:

1. **Identify the Scientist**: The question asks for the scientist who identified DNA as an acidic substance. Based on historical records, the scientist who first identified DNA was Friedrich Miescher in 1869. He discovered it while studying the composition of the cell nucleus.

**Hint**: Think about the historical context of DNA discovery and the key figures involved.

2. **Identify the Name Given**: Miescher named the substance he discovered "nuclein," which later came to be known as nucleic acid. However, in the context of the question, it is referred to as "Nucleon."

**Hint**: Recall the terminology used during the early studies of DNA and how it has evolved over time.

3. **Fill in the Blanks**: Based on the information gathered:
- X = Friedrich Miescher
- Y = Nucleon

### Final Answer:
X = Friedrich Miescher; Y = Nucleon