Final answer:
Firn is a compacted type of snow or ice with a grainy texture. The image representing firn is option (b) in Figure 13.1.5, showing water forming outside of a glass containing a cold beverage.
Step-by-step explanation:
Firn is a term used by geologists to describe a type of snow or ice based on its air content. It refers to snow that has been compacted over time and has a grainy texture. It lies between freshly fallen snow and glacial ice in the progression of snow metamorphism.
In the given options, the image that represents firn is option (b) in Figure 13.1.5. It shows water forming outside of a glass containing a cold beverage, which is similar to the compacted nature of firn.