The correct answer is C. Softer than diamond
Explanation:
Evan observation is related to the rock's hardness, which is usually measured on a scale from 1 to 10, in which 10 represents the hardest rock (diamond). In the case of the rock Evan found, the fact the rock can be scratched just using a fingernail shows the hardness of this rock is 2.5 or below because only minerals with this hardness can be scratched using the fingernail, while a higher hardness requires more complex tools.
Moreover, in this level of hardness, there are minerals such as gypsum or talc and these are softer than others such as feldspar with a hardness of 6 or diamond with a hardness of 10. In this context, it is safe to conclude this rock is softer than diamond. Also, hardness is not enough to determine if a rock contains two or more minerals or if it is metamorphic.
