Question

The blood gains its oxygen in which part of the body?

Answer 1

When you inhale, you breathe in air and send it down to your lungs. Blood is pumped from the heart to your lungs, where oxygen from the air you've breathed in gets mixed with it. That oxygen-rich blood then travels back to the heart where it is pumped through arteries and capillaries to the whole body, delivering oxygen to all the cells in the body -- including bones, skin and other organs. Veins then carry the oxygen-depleted blood back to the heart for another ride.

Answer 2

Lungs, or specifically alveoli? To add, I'd specify to say at the alveoli via diffusion through capillaries.