1 g of silicon contains ' n' atoms. how many atoms are there in 0.8 g of calcium?

Number of  moles = given mass/ molar mass
Given mass of calcium = 0.8 g
Atomic mass of calcium = 40g /mol
Number of moles = 0.8/40
                           = 0.02 mol
​1 mol = 6.022$\times$10 ²³ molecules
0.02 mol = 0.12044​$\times$10 ²³ molecules
Hence, 08g of calcium has ​0.12044​$\times$10 ²³ molecules.