(a) Hydrated aluminium oxide having dull luster
(b) Hydrated aluminium oxide having shining luster
(c) Hydrated aluminium oxide having vitreous luster
(d) Barium sulphate having vitreous luster

Ans. (a) : Hydrated aluminium oxide having dull luster

• Bauxite is hydrated aluminum oxide and has dull luster.
• It is a sedimentary rock with a relatively high aluminum content.
• Reddishbrown, white or tan in colour.