The word "firm" is an adjective used to describe something that is physically solid. For example, a firm pillow is one that is somewhat hard—as opposed to a very soft pillow. Sometimes, too, this word is used to describe someone's actions. For example, to say, "He was firm about his wish to have at least eight hours of sleep," means that the person did not give up his desire for the sleep (even if others protested).

“Fragile” means easy to break or"breakable_._" As for the other answer choices, “robust” means sturdy and strong; “stern” means enforcing the rules or strict; “firm” means strong or hard and not easily forced into a different shape; “logical” means rational or not breaking any of the rules of formal logic.

The word "compact" comes from root words meaning joined together. When we compact our garbage, we compress it into a small space. When we describe the garbage as being "compact," we are indicating that it is very densely packed together. "Dense" things do not have much air space. The same is true for compact materials.