**Core Concept**
Nucleic acids, such as DNA and RNA, exhibit maximum absorbance of ultraviolet (UV) light at 260 nm due to the presence of purine and pyrimidine bases (e.g., adenine, guanine, cytosine, thymine, uracil), which have conjugated double-bond systems that absorb UV radiation efficiently.

**Why the Correct Answer is Right**
The absorbance peak of nucleic acids occurs at 260 nm because the aromatic rings of purines and pyrimidines absorb UV light most strongly at this wavelength. This property is exploited in spectrophotometry to quantify DNA and RNA concentrations. The molar extinction coefficient of double-stranded DNA at 260 nm is approximately 660 µM⁻¹cm⁻¹, making it a standard in molecular biology.

**Why Each Wrong Option is Incorrect**
Option B: 280 nm – This wavelength is more characteristic of proteins (especially aromatic amino acids like tryptophan and tyrosine), not nucleic acids.
Option C: 410 nm – This is in the visible range and is associated with nucleic acid fluorescence or certain dyes, not intrinsic UV absorption.
Option D: 320 nm – This is not a significant absorption peak for nucleic acids and is more relevant to protein denaturation or photochemical reactions.

**Clinical Pearl / High-Yield Fact**
Always remember: **DNA/RNA absorb UV at 260 nm, proteins at 280 nm** – this is critical for spectrophotometric assays in labs. A 260/280 ratio >1.8 indicates pure DNA/RNA; values <1.8 suggest contamination with proteins.

✓ Correct Answer: A. 260nm