Question

Avogadro’s number is the number of molecules present in:
A. 1 g of molecule
B. 1 atom of molecule
C. 1 mole
D. 1 litre of molecule

Answer 1

Hint: Avogadro’s number is a special entity as it tells us the exact amount of the number of atoms present in exactly 12 grams of carbon- 12 which are equal to 6.023x${10}^{23}$ atoms. It is very important in everyday chemistry and so is studied separately.

Complete step by step answer:
- Matter is something which occupies space and has some specific mass. So it has the property of mass and volume. It is divided into solid, liquid and gas on the basis of its physical behavior and into pure substances and mixtures on the basis of chemical behavior.
- Pure substances are further classified into elements and compounds. Elements are made up of groups of the same molecules while compounds are made of groups of different molecules. Atom is the smallest unit of matter and contains a nucleus and orbits. Nucleus contains neutrons and protons and electrons revolve around it in different shells.
- So basically everything present in this universe is made up of atoms. The mass of an atom cannot be measured truly due to its very small size. So a relative term is used for it called relative atomic mass. Every atom has a mass which is related to hydrogen atom mass. Standard mass of hydrogen is 1 unit and to find the mass of any other atom, relative atomic mass is used.
$$Relativeatomicmass={\displaystyle \frac{mass\text{ of 1 atom of element}}{\text{mass of 1 hydrogen atom}}}$$
- Today a different unit is used which is based on the mass of 1 carbon-12 atom. It was adopted internationally in 1961 and according to it, relative atomic is given by
$$Relativeatomicmass={\displaystyle \frac{mass\text{ of 1 atom of element}}{{\displaystyle \frac{1}{12}}\text{x mass of 1 C- 12 atom}}}$$
- Mole is the amount of substance that contains the atoms, molecules or other particles in an entity equal to the atoms present in 12 g of C- 12 isotope. It defines the basis of physical chemistry and so its number is called Avogadro's number which is equal to 6.023x${10}^{23}$entities. It is denoted by the symbol $N_A$ .

Therefore, we can say that the Avogadro’s number is the number of molecules present in 1 mole and the correct option is C.

Note: Mole is not only related to mass but also to volume as any matter that has a certain mass will occupy a certain volume. 1 mole is the amount of molecules present in 22.4 litres of a gas calculated at standard temperature and pressure.