<u>The right choice is </u><u>Adding H2O(g) to the system</u>
<h2>Explanation:</h2>
If we dilute a solution by adding solvent like water, all of the concentrations will decrease and a change in Q occurs. If there are more species in solution that are products than reactants then Q will decrease. Hence the reaction will then shift towards the right side which is product side to reach equilibrium because there will be an increase the concentration of the reactants side.
Le Châtelier's principle states that when there is an dynamic equilibrium, and this equilibrium is disturbed by an external factor, the equilibrium will be shifted in the direction that can cancel the effect of the external factor to reattain the equilibrium.
<u><em>1) Removing H₂O(g) from the system:</em></u>
This will decrease the concentration of the reactants side, so the reaction will be shifted to the left side to suppress the removal of H₂O(g) from the system.
<u><em>2) Adding CH₃CHO(g) to the system :</em></u>
This will increase the concentration of the products side, so the reaction will be shifted to the left side to suppress the adding CH₃CHO(g) to the system.
<u><em>3) Removing C₂H₂(g) from the system:</em></u>
This will decrease the concentration of the reactants side, so the reaction will be shifted to the left side to suppress the removal of C₂H₂(g) from the system.
<u><em>4) Adding H₂O(g) to the system:</em></u>
This will increase the concentration of the reactants side, so the reaction will be shifted to the right side to suppress the addition of H₂O(g) to the system.
Chemists need the mole concept to bridge the gap between the microscopic world of atoms to the macroscopic world of humans. As you know, the molecular level consists of particles that are invisible to us.