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

Options

A. Rising `CO_(2)` concentration
B. Falling `CO_(2)` concentration
C. Rising `CO_(2)` and falling `O_(2)` concentration
D. Falling `O_(2)` concentration

Answer

A

Explanation

`CO_(2)` is released from blood in the lungs which are then expelled by and exhale. The urge to breath does not come from the need for oxygen but rather from the build-up of carbon dioxide.