Amount of $O_2$ normally carried by 100 ml of pure blood, is

The correct option is D 20 ml

Oxygen is carried in the blood either in dissolved form or in association with hemoglobin.

However, to calculate the concentration of oxygen transported in the blood, one needs to understand the amount of oxygen carried by each gram of hemoglobin. In a saturated condition, one gram of hemoglobin carries 1.34 ml of oxygen. Normally 100 ml of blood has around 15 gm of hemoglobin in it.

Thus, the amount of oxygen carried in 100 ml of pure blood can be calculated as 15 * 1.34 ml = 20 ml