Which term refers to the concept of being unrelated to religion and occurring once every hundred years?

The term that refers to being unrelated to religion is "secular." In a secular context, something is considered independent from religious influence or perspective, focusing instead on worldly or non-religious matters.

Additionally, the phrase "occurring once every hundred years" relates to the term "centennial," which describes events, anniversaries, or similar occurrences tied to a 100-year time span. However, since that specific aspect is not explicitly referenced in any of the options, it is important to note that the key focus here is on the first part of the term, which aligns perfectly with the meaning of "secular."

In relation to the other terms, "skeptical" pertains to doubt or disbelief, particularly about religious or philosophical claims; "sanctimonious" describes a show of being morally superior to others, often through a religious lens; and "solvent" relates to a substance capable of dissolving another, which is unrelated to both the concept of religion and a hundred-year timeframe.