Question

Which of the following is an example of an inclusion complex?

• A. Cyclodextrin–drug complex
• B. Iodine–potassium iodide
• C. EDTA–calcium
• D. Caffeine–benzoic acid

Hint:

An inclusion complex (also called a host–guest complex) forms when one molecule, the host, has a cavity in its structure that physically traps another molecule, the guest, inside it.

Answer 1

The Correct Option is A

Concept:
An inclusion complex (also called a host–guest complex) forms when one molecule, the host, has a cavity in its structure that physically traps another molecule, the guest, inside it. There is no normal chemical bond between them — the guest simply sits inside the host's cage held by weak forces like van der Waals interactions and hydrophobic effects.

Step 1: Look at cyclodextrins. These are ring-shaped (cyclic) sugar molecules that look like a hollow truncated cone. The outside is water-loving while the inside cavity is water-hating, so a poorly water-soluble drug molecule can slip into that cavity. This is the classic textbook example of an inclusion complex and is widely used in pharmacy to improve drug solubility and stability.

Step 2: Compare the others. Iodine–potassium iodide forms the I₃⁻ triiodide ion (a chemical interaction, not a host trapping a guest). EDTA–calcium is a chelation complex where EDTA grabs the metal with several donor atoms. Caffeine–benzoic acid is a molecular association/complex but not a true cavity-based inclusion. None of these involve one molecule being physically caged inside another.

Answer: Option (1) — the Cyclodextrin–drug complex is the correct example of an inclusion complex, because the drug guest sits inside the cyclodextrin host cavity. (1)