1 mole of any substance contains Avogadro's number.
So, 1 mole of O2= 6.023x10^23 molecules
3 mole of O2= 6.023x10^23x3 molecules
= 1.8069x10^24 molecules
Each molecule of Oxygen has 2 atoms.
therefore,
1.8069x10^24 molecules= 1.8069x10^24 x 2 atoms
= 3.6138x10^24 atoms.
The concentration of [CI-] : 0.617 M
<h3>Further explanation</h3>
FeCl₃ dissolved in 450 mL of solution(will dissociate )
Reaction
FeCl₃⇒Fe³⁺+3Cl⁻
- mol FeCl₃(MW=162,2 g/mol)



Emperic formula is SO subscript 2. Molecular formula would be SO subscript 2 multiply 1 so it's the same answer.
Because lager objects have much more room for mass the smaller objects. take the earth as an example the earth is very big and has alot of mass in it which makes gravity that pulls us down when we jump up.