Why is resolution improved in frozen samples compared to liquid samples?

Resolution is significantly improved in frozen samples primarily because molecules are fixed in place. When a sample is frozen, the molecular motion is greatly reduced. As a result, there is less thermal agitation compared to molecules in a liquid state, where they can move freely and collide with one another. This reduction in movement helps maintain a more stable structure, allowing for clearer imaging and better resolution in techniques such as cryo-electron microscopy or X-ray crystallography.

The other options do mention aspects that relate to molecular behavior in both states; for instance, while it's true that molecules do move slower in a frozen state, the critical factor for resolution is that they are essentially immobilized. Additionally, the size of the molecules does not inherently increase simply due to the phase change, and while it is true that liquid samples are generally at a relatively higher temperature which contributes to increased molecular motion, it is the immobilization of the molecules in the frozen state that fundamentally enhances resolution. Therefore, the ability to capture a clearer image of the sample due to fixed molecular positions is the key reason why frozen samples yield better resolution.