The number of atoms of chlorine present in 5.85g of NaCl is (Na=23,Cl=35.5) 2. 2.25g of an oxide of copper on reduction gave 2.00g of copper. Another oxide (2.50g) also gave 2.00g of copper. These results illustrates the law of:

In one molecule of NaCl, there is one atom of Cl. Therefore, 0.1 mol of NaCl contains 0.1 mol of Cl atoms.

Using Avogadro's number ($6.022 \times 10^{23}$ atoms/mol):

The number of atoms of chlorine present in 5.85g of NaCl is $\boxed{\text{6.022} \times 10^{22} \text{ atoms}}$.

2. Step 1: Analyze the first oxide of copper. Mass of oxide = 2.25 g Mass of copper = 2.00 g Mass of oxygen = Mass of oxide - Mass of copper

Ratio of copper to oxygen in the first oxide:

Mass of oxide = 2.50 g
Mass of copper = 2.00 g
Mass of oxygen = Mass of oxide - Mass of copper

Ratio of copper to oxygen in the second oxide:

For a fixed mass of copper (2.00 g), the masses of oxygen that combine with it are 0.25 g (in the first oxide) and 0.50 g (in the second oxide).
The ratio of these masses of oxygen is:

This ratio (2:1) is a simple whole number.

This observation illustrates the Law of Multiple Proportions. This law states that if two elements can combine to form more than one compound, then the ratios of the masses of the second element that combine with a fixed mass of the first element are ratios of small whole numbers.

These results illustrate the law of: $\boxed{\text{Multiple Proportions}}$.