Select the correct option:
The board will convene next Friday, ___ final approval is expected.

Correct option is C

The correct substitution of the highlighted words is (c) when.
Here, “next Friday” is a time expression, and the clause “final approval is expected” describes what will happen at that time. For time reference, the most natural relative connector is when: “next Friday, when final approval is expected.” It links the time and the event smoothly without needing an explicit preposition.
Grammatical rule used:
· Use when to introduce a relative time clause referring to a time noun (day, year, moment, etc.).
· Use where for place nouns; which + preposition is used when a specific preposition relationship is intended and sounds natural.
Example: We met on a day when the entire city was celebrating.
Information booster / exception:
· “on which” can be grammatically possible with days ( Friday, on which…), but it is more formal/less natural here; when is the best fit for standard exam usage and fluency.
· “whereupon” means “immediately after which / as a result of which,” usually showing sequence/result, not simply time scheduling.