The term meaning "theoretical; lacking substance" is ...

• A. Abstract
• B. Futile
• C. Diverse
• D. Pernicious

Answer: (A)

The main idea here is identifying a word that describes ideas rather than things you can touch. Abstract refers to concepts that exist in thought and general principles rather than in a physical, concrete form. When something is abstract, it’s often theoretical and not tied to material substance, which is why it fits the clue “theoretical; lacking substance.” For example, notions like justice or happiness are abstract ideas; they’re discussed and analyzed but aren’t tangible objects you can hold.

Why the other options don’t fit as well: futility or being futile describes something useless or pointless, focusing on usefulness rather than whether something is conceptual or physical. Diverse means showing variety, which isn’t about being theoretical or lacking substance. Pernicious means harmful or damaging, which conveys harm rather than a lack of concrete substance or theory.

So the term that best matches “theoretical; lacking substance” is abstract.