Which of the following is not an ore of aluminium ?

ANS:A - Troosite

Of the options provided, "Kaolin" is not an ore of aluminum. Kaolin is a type of clay mineral composed mainly of kaolinite, and it is used in various industries such as ceramics, paper making, and cosmetics. The other options - Alunite, Cryolite, and Troosite (assuming it's a valid mineral name) - are associated with aluminum ore deposits or have aluminum-bearing compounds. Alunite is a mineral containing aluminum, Cryolite is a mineral used in the production of aluminum, and Troosite (if it exists) would potentially be an aluminum-bearing mineral. Therefore, "Kaolin" would be the correct answer to your question.