The rate of the backward reaction increases
Explanation:
It is evident that if the reaction is left to proceed spontaneously, the forward reaction is favored because it results in a decrease in pressure in the system (The total reactants have 5 moles and the products have 3 in total).
Increasing H₂O concentration is then reaction, therefore, stymies the forward reaction and favors the reserves reaction. This is because the reverse reaction will lead to reduced pressure.
You would need 1000 liters
I'm pretty sure all 4 are subatomic particles but if i had to guess i'd be Photons