Answer: The unknown mineral is softer than topaz and diamond both.
Explanation:
Mohs scale is scale used to measure the hardness of the minerals. the value of the scale is from 0 to 10. The mineral with higher value on scale will be able to scratch easily the mineral with lower value on the scale.
As according to the question,Topaz has Mohs hardness of 8 and was able to scratch the unknown mineral which implies that the unknown mineral is softer than the Topaz .And Topaz is softer than Diamond which means that unknown mineral is also softer than diamond.
