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Which of the following statements about the process of respiration is/are correct?
I. During inspiration, the diaphragm gets relaxed.
II. During expiration, external inter-costal muscles contract.
III. A healthy human adult breathes 12-16 times per minute at rest.
Select the answer using the code given below.
Explanation
Statement I is incorrect. During inspiration (inhalation), the diaphragm contracts and moves downwards, increasing the volume of the thoracic cavity to allow air to enter the lungs.
Statement II is incorrect. The external inter-costal muscles contract during inspiration to lift the ribs and sternum. During normal expiration, these muscles relax, allowing the rib cage to return to its original position due to elastic recoil.
Statement III is correct. According to standard biological texts (like NCERT), a healthy human adult breathes on average 12–16 times per minute at rest.