Question

How can I find the volume of $3\times {{10}^{25}}$ molecules of Neon gas at STP?

Answer 1

Mole, also pronounced as mol is a standard scientific unit used for measuring large quantities of very small entities such as atoms, molecules, or some other specified particles.

Complete answer:
Avogadro's number is the number of units present in per mole of any substance (defined as its molecular weight in grams), and is equal to the value $6\times {{10}^{23}}$. The units mentioned above may be electrons, atoms, ions, or molecules, depending on the nature of the substance and the character of the reaction (if any).
The value of the Avogadro constant was chosen such that the mass of one mole of a chemical compound, in grams, is numerically equal to the average mass of one molecule belonging to the compound, and is generally measured in daltons.
Atomic no is defined as the total no of protons present in the nucleus of an atom or total no of electrons present in the orbits surrounding the nucleus.
Mass number is defined as the total no of protons and neutrons present in the nucleus of an atom.
Volume is defined as the amount of space occupied by a substance, while mass is defined as the amount of matter that it contains. The amount of mass per unit of volume is called density.
S.I unit of volume is the meter cube.
Now the molar mass of Neon is 20g.
$6\times {{10}^{23}}$ molecules of Ne occupies 22.4 L
So, $3\times {{10}^{25}}$ molecules of Ne occupies $(\dfrac{3\times {{10}^{25}}}{6\times {{10}^{23}}})\times 22.4\,L$.

Note:
That long number is known as Avogadro's number after the first scientist Amadeo Avogadro in the nineteenth century. The mass of 1 mole of something in grams is the mass of that substance in mass units.