Topic: Interchange of Parts of Speech,

Best Answer Explained in Below-:

The term 'rigidity' is a noun that refers to the quality or state of being stiff, inflexible, or resistant to change. To determine its corresponding adjective, we must look for a word that describes this quality. Among the options provided, 'rigid' is the correct answer.

Option B, 'rigid,' is the direct adjective form associated with 'rigidity.' It describes something that is stiff and unable to change shape, which aligns with the meaning of 'rigidity.' For instance, we might say, "The rigid structure of the building ensures it withstands strong winds."

Option A, 'rigor,' relates to strictness or severity but does not directly describe the state of being rigid. Option C, 'rigorous,' refers to something that is thorough and accurate, often used in contexts like 'rigorous testing' and does not pertain to physical stiffness. Finally, option D, 'rigidness,' although related, is a noun form and not an adjective.

Thus, 'rigid' accurately represents the characteristic described by 'rigidity,' making it the correct choice.