The option that identifies the context clue that would be most helpful in determining the meaning of the underlined word is remarkable no so much for...as for their senseless brutality, here we have a contrast with the use of the word as between the descriptions, senseless brutality is a negative description and since we are talking about the use of comparison the meaning of munificence has to be positive according to the context.
In fact, munificence is a positive word it is a synonym of generosity, in this way the expression remarkable no so much for...as for their senseless brutality is the clue that helps you understand the meaning of the word.
The other options are not correct because they don't have a direct connection with the specific word we want to understand.