Final answer:
The closest voltage corresponding to the given conditions is approximately 2.5 V based on the standard cell potentials that are described as spontaneous, which is option b.
Step-by-step explanation:
To determine the voltage corresponding to the given conditions, we need to evaluate the information provided about cell potentials under different scenarios. We have a couple of options for standard cell potentials that are spontaneous, and several for conditions that are nonspontaneous. If we look closely, we can see that the closest value to the options provided (1.922 V, 2.5 V, 3.0 V, and 4.0 V) appears in the mention of standard cell potential values that are spontaneous. The standard cell potential under spontaneous conditions that is close to one of the options is +2.115 V from item 21(a). Based on this, the most appropriate answer would be approximately 2.5 V, making option b the correct choice.