A material like steel is inflexible and would be considered rigid.  Thus, the best way to characterize something rigid is to term it as stiff.

Something that is "firm" holds its form easily and is difficult to bend out of shape. The word that best reflects this characteristic as a synonym is therefore "stiff," which means inflexible. The other answer choices are unrelated to the word "firm."

Something that is "frail" is easily broken. Something that is "weak" is lacking strength, and therefore also breaks very easily. Given the similarities between these two words, "weak" is the best synonym for "frail."

A person who appears "unkempt" looks messy, as if he or she has not groomed themselves, and generally lacking in personal maintenance. Have you ever left for school in a hurry, perhaps with unbrushed hair or wrinkled clothes? You likely seemed unkempt. Now that we know the meaning of the given term, let's examine the choices. "Tidy" means neat and organized, so it cannot be our answer. "Forceful," which means powerful, and "mistaken," which means incorrect, are not related to an untidy appearance. We are left with "disheveled," which means physically messy or out of order. We have found our synonym!

Something that is "compressed" is forced into a smaller space. Something that is "condensed" is reduced from a larger size into a smaller size while still holding the same amount of material. Given the similarities between these two words, they are synonyms.

The word "vivid" means very bright or lively. "Bright" is the best choice because it is a part of the definition of "vivid." Considering the other choices, "new" is unrelated in meaning to "vivid," "sight" is a noun that means the ability to see, and "cloudy" means foggy or unclear.

The word "blaring" is used to describe a very loud sound. Notice that several options have to do with being loud—"loud," "noisy," and "deafening." It is only the last option that is acceptable. When something is "deafening," it is so loud that it makes you lose your ability to hear. This is much better than the rather standard "loud" and "noisy." If there were no other options, these would be fine; however, it is best to match the intensity and pick "deafening."

Whenever something is an "illusion," it appears one way, though the reality is really something else. For example, you could say, "Peter's many books gave the illusion that he was very intelligent, when he in fact did not know much at all!" The only option that expresses this idea is "appearance." This is not always going to be a synonym for illusion, but in this case, it functions well enough, given that no other options are as good as this one.

"Timid" means showing a lack of confidence or courage, therefore "shy" would be the word most like "timid."

"Visible" means able to be seen. The best choice is "noticeable," which means able to be noticed. Something that is "noticeable" can be seen. Considering the other choices, "permeable" means full of small holes so certain things may pass through, "cloudy" means not clear, and "vision" is sight. Even though "vision" is related to "visible," it is a noun while "visible" is an adjective. Since "noticeable" is both close in definition to "visible" and an adjective, it is the best choice.