Option 1 -> "therefore" indicates consequence, but spending money isn't a result of being a miser.
Option 2 -> "although" shows contrast but typically comes at the beginning of the clause ("Although he is a miser, he spent...").
Option 3 -> "whereas" compares differences between two things, not an unexpected action despite a characteristic.
Option 4 -> "nevertheless" means "in spite of that/however," perfectly showing the contrast between being miserly yet spending lavishly.
Hence, Option 4: nevertheless -> This conjunctive adverb correctly expresses that despite his miserly nature (reluctance to spend), he unexpectedly spent a large amount on his daughter's marriage, highlighting the contradiction between his character and his action -> correct