heating the sample on a hot plate scratching the sample with a nail hitting the sample with a hammer shining a bright light on the sample
I gave my students this multiple choice question: Which of the following actions is most likely part of a test to find the hardness of a mineral sample?

Only one answer is correct among these 4 choices:
- heating the sample on a hot plate
- scratching the sample with a nail
- hitting the sample with a hammer
- shining a bright light on the sample

Could you tell me which one is correct?

scratching the sample with a nail