Nucleotide arrangement in DNA can be seen by

Options

A. X - ray crystallography
B. electron microsecope
C. ultracentrifuge
D. light microscope

Explanation

### Step-by-Step Solution:

1. **Understanding Nucleotide Arrangement**:
- Nucleotides are the building blocks of DNA, consisting of a sugar, a phosphate group, and a nitrogenous base (which can be a purine or a pyrimidine). The arrangement of these nucleotides forms the structure of DNA.

2. **Structure of DNA**:
- The DNA structure is a double helix, where two strands run in opposite directions. Each nucleotide connects to the next through the sugar and phosphate backbone, while the nitrogenous bases pair with each other (adenine with thymine and guanine with cytosine).

3. **Techniques to Observe Nucleotide Arrangement**:
- The arrangement of nucleotides in DNA can be visualized using specific scientific techniques. One of the most prominent methods is X-ray crystallography.

4. **X-ray Crystallography**:
- This technique involves crystallizing the DNA molecule and then directing X-rays at the crystal. The X-rays scatter upon hitting the atoms in the DNA, creating a diffraction pattern that can be analyzed to determine the arrangement of the nucleotides.

5. **Historical Context**:
- The discovery of the DNA structure using X-ray crystallography was significantly advanced by the work of James Watson and Francis Crick. They used data from X-ray diffraction images produced by Rosalind Franklin to propose the double helix model of DNA.

### Final Answer:
The nucleotide arrangement in DNA can be seen by **X-ray crystallography**.

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