The baby cried most of _ night.

Explanation

The definite article "the" is used before singular or plural nouns when we are referring to something specific that is known to the speaker and listener or has been previously mentioned or is identifiable from the context.In the Sentence:"The night": This refers to a specific night, in this case, the night during which the baby cried.Therefore, "the" is appropriate here because the speaker is referring to a particular night (the one during which the baby cried), which is identifiable and specific within the context.