Answer:
C but read the limitation
Step-by-step explanation:
Gold sample
Color wouldn't tell you much. In fact it may fool you. Fool's Gold is the same color as gold.
Gold is very malleable. That's what hitting gold with a hammer will do. It tends to shape the gold without destroying it into lots of pieces. A lot of yellow things have that property.
If only it was that simply. Yes if you are sure there is gold in that location. You have to pick this answer, because the other 2 don't work. So this is possible, but not the best way. The best way is to subject the sample to chemical treatment. If you are left with a yellow sample, then you could make the case for it being gold.