(a)

Given Data :

Given mass of carbon = 12 g

Step 1 : Calculate the number of moles in 12 g of carbon - 12 element.

Number of moles of carbon $=\frac{\text{ given mass of carbon }}{\text{ Atomic mass of carbon }}$

Number of moles of carbon $=\frac{12}{12}$

Number of moles of carbon = 1 mole

  Step 2 : Calculate the number of atoms in 12 g of carbon - 12 element.

Number of moles of carbon $=\frac{\text{ Number of atoms }}{6.022\times {10}^{23}}$

Number of atoms = 1 × 6.022 × 10²³ = 6.022 × 10²³

Conclusion :

Therefore, 6.022 × 10²³ atoms are there in exactly 12 g of carbon-12 element.

(b)

The name given to this number is Avogadro's number.

Avagadro's number = 6.022 × 10²³

(c)

1 mole of substance contains this number of atoms.

1 mole = 6.022 × 10²³ number of atoms