AI-generated practice question — model-generated for extra practice, not a previous-year CBSE board question.
The balloon-like structures in the lungs where exchange of gases takes place are called alveoli (singular: alveolus).
The examiner expects the term "alveoli." These are tiny air sacs with thin walls and a rich network of blood capillaries, enabling efficient exchange of O₂ and CO₂. Just one word/term is sufficient for 1 mark, but naming them as "balloon-like air sacs called alveoli" is safer.