The complete oxidation of one molecule of PGAL (phosphoglyceraldehyde) requires a total of 6 oxygen atoms.

Explanation:

1. What is PGAL?
PGAL is an intermediate molecule formed during the process of glycolysis, which is the breakdown of glucose in the cytoplasm of cells. It is also involved in the Calvin cycle, a series of reactions that occur during photosynthesis.

2. Oxidation of PGAL:
During the oxidation of PGAL, each molecule undergoes a series of reactions that result in the production of energy-rich molecules such as ATP (adenosine triphosphate) and NADH (nicotinamide adenine dinucleotide). These reactions also involve the reduction of electron carriers and the release of carbon dioxide.

3. Oxygen requirement in oxidation:
In the process of complete oxidation, each carbon atom in PGAL is converted into carbon dioxide. Since PGAL contains 3 carbon atoms, three molecules of carbon dioxide are produced. Each carbon dioxide molecule consists of one carbon atom and two oxygen atoms.

4. Calculation:
To calculate the total number of oxygen atoms required for the complete oxidation of one molecule of PGAL, we can multiply the number of carbon dioxide molecules produced (3) by the number of oxygen atoms in each carbon dioxide molecule (2).

3 (CO2) x 2 (O) = 6 oxygen atoms

Therefore, six oxygen atoms are required for the complete oxidation of one molecule of PGAL.

In conclusion, the correct answer is B) 6.