Which word creates a related form by adding a prefix to the base word of mobility?

Answer and explanation:

Even though you haven't provided us with any options to answer this question, we can reach a plausible conclusion from the question itself. The base word for mobility is mobile. Mobile refers to something that is able to move freely. Mobility was formed by adding the suffix -ity to the base word.

Now, we are being asked to add a prefix to mobile. Even though there are several prefixes with different meanings, there is one that is commonly attached to the word mobile: the prefix im-. Im- is a negative prefix, transforming the word to which it is attached into a denial of its meaning. If something that is mobile is something that can move freely, something that is immobile is its opposite. Immobile means motionless or incapable of moving.

We do not see other prefixes (des-, un-, a- etc.) attached to the word mobile. Therefore, we can safely conclude the best answer to this question is "immobile".