The visible universe is estimated to contain $10^{22}$ stars. How many moles of stars are present in the visible universe?

Calculate the number of atoms in:
$(i)$ $0.02$ moles of carbon
$(ii)$ $30$ grams of carbon
$(iii)$ $6$ moles of aluminium ions.

Which of the following represents $1 \, u$?

Explain the following with one example of each:
$(i)$ Atomic number
$(ii)$ Mass number

If an ion $M^{3+}$ contains $10$ electrons and $14$ neutrons, what are the atomic number and mass number of the element $M$?

Calculate the number of atoms in $120 \, g$ of calcium and $120 \, g$ of iron. Which one has more number of atoms and what is the difference? (Given: atomic mass of calcium $= 40 \, u$ and iron $= 56 \, u$)