物理的問題

What is your meaning of "重"?

If you are talking their weight. It will depends on their volume and using the following equation:

Weight = Density * Volume

If you are talking about their molecular mass. Their molecular mass are as the following:

Aluminium - 13
Iron - 26
Copper - 29
Titanium - 22

Copper will be the heaviest than Iron, Titanium & Aluminium correspondingly if the parameter, volume, is constant.

在同一體積中，誰的密度最大就是最重。

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