Question

How many moles of ${O_2}$ are there in $2500g$ of ${O_2}$?

Answer 1

The mole (symbol: mol) is the unit of measurement in the International System of Units for the quantity of substances (SI). It is described as precisely $6.02214076 \times {10^{23}}$ particles that can be atoms, molecules, ions, or electrons.
In the periodic table, oxygen is a member of the chalcogen group, a highly reactive non-metal and an oxidising agent that easily forms oxides with most elements and other compounds. Oxygen is the third-most abundant element in the universe by mass, after hydrogen and helium.

Complete step by step answer:
Mole is a number that connects the mass of a substance with its number of particles.
For all substances, the number of atoms or other particles in a mole is the same. The mole is connected in the following way to the mass of an element: one mole of carbon-$12$ atoms has $6.02214076 \times {10^{23}}$atoms and a mass of $12$ grams. For contrast, by definition, one oxygen mole consists of the same number of atoms as carbon-12, but it has a mass of $15,999$ grams.
Accordingly, oxygen has a greater mass than carbon. It is possible to extend this logic to molecular or formula weights as well.
One mole of a substance = $6.02 \times {10^{23}}$ particles (entities)
One mole of Dioxygen or ${O_2}$ = $6.02 \times {10^{23}}$ molecules of ${O_2}$
One mole of ${O_2}$ has mass $32g$
we can say that
$32g$ of ${O_2}$ =$1mole$
$1g$of ${O_2}$ = $\dfrac{1}{{32}}$mole
$2500g$ of ${O_2} = \dfrac{1}{{32}} \times 2500$= $78.125$ moles.

Note:
Two atoms of the element bind to form dioxygen at standard temperature and pressure, a colourless and odourless diatomic gas with the formula ${O_2}$. $20.95$ percent of the Earth's atmosphere constitutes diatomic oxygen gas. In the form of oxides, oxygen makes up almost half of the Earth's crust.
A substance's molar mass is the mass of 1 mole of that substance, in gramme multiples. The number of moles in the sample is the volume of material. The magnitude of the molar mass is numerically the same for most practical purposes as that of the mean mass of one atom, expressed in daltons.