A spontaneous process is capable of proceeding in a given direction without needing to be driven by an outside source of energy. A Spontaneous reaction takes place on its own without external influences. In a spontaneous reaction, this change in entropy is positive (ΔS) , the change in enthalpy is negative (ΔH) and most importantly the
value of ΔG(change is free energy) is negative.
In order to decide the spontaneous reaction among the options, we consider the relative electrode potentials of the reaction species. The specie having a more negative reduction potential can displace the other specie from its aqueous solution. Since the reduction potential of Mn^2+ is -1.19 V while that of nickel is -0.25 V, it follows that manganese can spontaneously displace Ni^2+ from its aqueous solution as shown in the answer above.
c) more particles collide with the walls of the container
Explanation:
More moles means more particles. If the volume remains the same, the collisions of more particles with the container walls cause the pressure to increase.