Option B is the correct answer because 'valuable' means 'worth a great deal of money' whereas 'worthless' means 'having no use or value'. Thus, option B is the most appropriate word opposite in meaning to the given word.
Option A is incorrect because 'invaluable' means 'very useful' whereas 'valuable' means 'worth a great deal of money'. It is similar in meaning hence option A is not the appropriate word opposite in meaning to the given word.
Option C is incorrect because 'priceless' means 'of great value' whereas 'valuable' means 'worth a great deal of money'. It is similar in meaning hence option C is not the appropriate word opposite in meaning to the given word.
Option D is incorrect because 'expensive' means 'very costly'. Thus, option D is not the appropriate word opposite in meaning to the given word.