Was Crocodile stronger at Marineford? Or was he holding back in Alabasta?

 During the Alabasta arc, Crocodile displayed a level of power that was initially considered overwhelming by the Straw Hat Pirates. He possessed the Logia-type Devil Fruit called the Suna Suna no Mi (Sand-Sand Fruit), which granted him the ability to control and transform into sand. He had a reputation as a Shichibukai and controlled the desert kingdom of Alabasta from the shadows. His strength was showcased through his battles with Luffy and others. At Marineford, Crocodile was present as part of the war that took place at Marine Headquarters. While he did participate in the battle, he didn't display the same level of dominance as some other powerful characters present. This has led fans to speculate that he might not have been as strong as initially portrayed in Alabasta. It's important to note that power scaling and character abilities can be subject to interpretation and development by the author. Oda often keeps details deliberately open-ended to keep the story intriguing.

What is the molecular mass of O2?

 Molecular mass is a measure of the mass of a molecule and is calculated by adding together the atomic masses of all of the atoms in the molecule. In the case of oxygen gas (O2), the molecular mass is calculated by adding the atomic mass of two oxygen atoms, which is 16.0 g/mol for each oxygen atom. The total molecular mass of O2 is therefore 2 x 16.0 g/mol = 32.0 g/mol.

It is important to note that the atomic mass of an element is the average mass of the atoms of that element, as measured in atomic mass units (amu). The atomic mass of an element is typically given in the periodic table of elements and is based on the relative abundance of the different isotopes of that element in nature. The atomic mass of an element can be used to calculate the molecular mass of a compound by adding together the atomic masses of all of the atoms in the compound.