1. calculate the ratio of atoms present in 4g of magnesium and 4g of iron. (Mg = 24, Fe = 56 ) 2. what is th mass in grams of each of the following ? (a) 1.0 mole of Cu (b) 0.5 mole of S (c) 6.022 x 10^23 atoms of Ca 3. calculate the weight of one atom of hydrogen.

1) Molar mass of magnesium = 24 g
Molar mass of iron = 56 g
24 g of magnesium contains = 6.022$\times$10²³ atoms

4 g of magnesium = $\frac{6.022\times {10}^{23}}{24}\times 4$

56 g of iron contains = 6.022$\times$10²³ atoms

4 g of iron = $\frac{6.022\times {10}^{23}}{56}\times 4$

Ratio of 4 g of Mg and 4 g of Fe = 7 : 3

2) a) Number of moles (n) = $\frac{\text{Given mass}}{\text{Molar mass}}$

1 mole of Cu = $\frac{\text{Given mass}}{63.5}$

Mass of Copper = 1$\times$63.5 = 63.5 g

b) 0.5 mole of S

0.5 = $\frac{\text{Given mass}}{32}$

Mass of S = 0.5$\times$32 = 16 g

c) n = $\frac{\text{Number of particles} }{\text{Avagadro number}}$

n = $\frac{6.022\times {10}^{23}}{6.022\times {10}^{23}}$ = 1 mole

1 = $\frac{\text{Given mass}}{\text{Molar mass of Ca}}$

Given mass = $1\times 40$ = 40 g

3) 6.022$\times$10²³ atoms of hydrogen weighs = 1 g

1 atom of hydrogen weighs = $\frac{1}{6.022\times {10}^{23}}$ = 0.166$\times$10^-23 g