When you hold your breath, which of the following gas changes in blood would first lead to the urge to breathe?

Step-by-step solution

The rise in C O 2 concentration stimulates chemoreceptors present in the aorta and carotid artery, which stimulates the respiratory centre. The respiratory centre is not directly sensitive to oxygen concentration & hence desire to breathe is induced by rising in C O 2 the concentration of blood.