Questions: Nucleic acids absorb light strongly in the ultraviolet region of the spectrum because they have double-bond systems. Unsaturated Unconjugated Conjugated Saturated

The answer is the third one: Conjugated.

Explanation for each option:

1. Unsaturated: While nucleic acids do contain unsaturated bonds, the term "unsaturated" refers to the presence of double or triple bonds in general, without specifying their arrangement. This does not specifically explain the strong UV absorption.

2. Unconjugated: Unconjugated systems have isolated double bonds that do not interact with each other. Such systems do not absorb UV light as strongly as conjugated systems because the electrons are not delocalized over multiple atoms.

3. Conjugated: This is the correct answer. Conjugated systems have alternating single and double bonds, which allow for electron delocalization across the system. This delocalization lowers the energy gap between the ground and excited states, resulting in strong absorption in the UV region.

4. Saturated: Saturated compounds contain only single bonds and do not absorb UV light strongly because they lack the necessary electronic transitions associated with double bonds.

In summary, nucleic acids absorb light strongly in the ultraviolet region due to their conjugated double-bond systems, which allow for electron delocalization and lower energy transitions.