At the site of gas exchange in the lungs, where does the oxygen move?
o2 moves from the alveoli to the white blood cells.
o2 moves from the white blood cells to the alveoli.
o2 moves from the alveoli to the red blood cells.
o2 moves from the red blood cells to the alveoli.

The correct answer would be O₂ moves from the alveoli to the red blood cells.

Around 97% of the oxygen is transported with the help of red blood cells (RBC) in the blood while the rest is transported in a dissolved state through plasma.

Oxygen is carried by hemoglobin present in the red blood cell.

It can bind with oxygen in a reversible manner to form oxy-hemoglobin.

At alveolar site, partial pressure of oxygen is high and that of carbon dioxide is less. In addition, H⁺ ion concentration and temperature are also less. All these factors lead to the formation of oxy-hemoglobin at this site.

At tissue level, conditions are reversed (less oxygen pressure and high carbon dioxide pressure et cetera) which lead to the dissociation of oxygen from hemoglobin and thus it is released into the tissue or cell.

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.