Correct Answer: Definite

Solution : The third option is the correct answer.

"Elusive" refers to something that is difficult to grasp, catch, or define. It suggests a lack of clarity or certainty. On the other hand, "definite" means clearly defined, certain, and not ambiguous, representing the opposite quality.

The meanings of the other options are as follows:

Explosive refers to an explosion or is characterised by the sudden and violent release of energy.

Affordable means inexpensive, within one's financial means.

Rigid means lacking flexibility or adaptability.

Therefore, the correct answer is definite.