Question

calculate no. of atom in

• 5.2 gram of helium
• 5.2 unit of helium(given -atomic mass of helium 4u and 1 mole of helium has mass of 49.)

Answer 1

1) Atomic mass of He = 4 u
Helium has 4 units .
4 g of He contains = 6.022$\times$ 10²³ atoms
5.2 g of He contains = $\frac{6.022\times {10}^{23}}{4}\times 5.2=7.82\times {10}^{23}atoms$

2) 1 atom of He contains = 4 units
4 units of He has atoms = 6.022$\times$10²³atoms
5.2 g of He = 7.82$\times$ 10²³ atoms