Which one among the following is the correct nature of the substance filling up the pleural cavity?

Correct option is A

The correct answer is (a) Liquid
Explanation:
• Normal pleural cavity contains a thin layer of pleural fluid (liquid) between visceral and parietal pleura.
• Fluid lubricates and reduces friction during respiration.
• Surface tension of fluid helps lungs adhere to thoracic wall.
• Presence of air (pneumothorax) or excess fluid (pleural effusion) is pathological.
Information Booster:
• Pleural fluid is secreted by mesothelial cells of pleura.
• Volume is small—excess causes breathing difficulty.
Additional Knowledge:
(b)/(c) Air in pleural space indicates pathology.
(d) Fatty muscle — not anatomically correct.