Blood arriving at the right atrium is de-oxygenated.

Yes, that's correct. Blood arriving at the right atrium is deoxygenated. This blood has circulated around the body, delivering its oxygen to the various cells and tissues. The deoxygenated blood is then returned to the heart via the veins, entering the right atrium. From the right atrium, the blood is pumped into the right ventricle and then to the lungs where it is re-oxygenated. The oxygen-rich blood then returns to the heart, entering the left atrium. From the left atrium, the blood is pumped into the left ventricle and then out to the body, starting the cycle again.