Nupur wants to find out which is harder: a big candle or a small iron key
Nupur wants to find out which is harder: a big candle or a small iron key. She says the fair test is to try scratching each one with the other. Pranav says there's no need — just weigh them; the big candle is heavier, so it must be harder. Who is thinking about it correctly?
Who do you think is right? Pick one.
The answer: Nupur is right, hardness is tested by scratching, not by weighing
Why
Pranav is mixing up two different properties. Weight tells you how much stuff there is; hardness tells you how easily a material can be scratched or pressed in. The big candle is heavier only because it is big — and yet a fingernail can dig into its wax. The key is small and light, yet a fingernail can't dent it at all. So the heavier object here is actually the softer one. That is why Nupur's scratch test is the fair one: whichever material leaves a scratch on the other is the harder material, however big or small each piece is. Test: drag the tip of the key across the candle — it carves a clear groove; now try to scratch the key with the candle — nothing happens. Nupur is right: hardness is about resisting scratches, so materials are compared by scratching, not by weighing.
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