When you hold your breath, which of the following gas changes in blood would first lead to the urge to breathe?
1. Falling O2 concentration
2. Rising CO2 concentration
3. Falling CO2 concentration
4. Rising CO2 and falling O2 concentration

Subtopic:  Respiratory System: Regulation of Respiration |
 61%
NEET - 2015
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NEET 2026 - Target Batch - Vital
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