Which of the following factors can lead to a marriage being declared void?

A marriage can be declared void if it is established that one of the parties was already legally married to someone else at the time of the second marriage. This condition, known as bigamy, directly contradicts the legal principles surrounding marriage, which require that each party be free to marry. In essence, bigamy undermines the fundamental nature of marriage as a union between two individuals, making the second marriage invalid from the outset.

In contrast, the other options do not have the same legal ramifications as bigamy. For example, failure to file married tax returns does not affect the validity of the marriage itself, but rather pertains to tax obligations. Disagreement over finances is a common issue in marriages but is also not sufficient to declare a marriage void; it may lead to disputes but does not impair the legal standing of the marriage. Similarly, separation prior to annulment does not render a marriage void; rather, it may be part of the annulment process, which is a separate legal action that can dissolve a marriage under specific circumstances.