The correct option is B troublesome
Convenient means suitable or agreeable to the needs or purpose; well-suited with respect to facility or ease in use; favorable, easy, or comfortable for use. The opposite of convenient is troublesome, or difficult. Hence, Option C is correct. Among the rest of the options, inadvisable means likely to have unfortunate consequences, objectionable means wished for as being an attractive, useful, or necessary course of action, desirable means wished for as being an attractive, useful, or necessary course of action. These options do not express the antonym, hence incorrect.