Which of the following, when hammered, can become a powdery mass?

Carbon

The correct answer is option 2. Carbon.

Out of the listed options, the one that turns into a powdery mass when hammered is: Carbon

Here's why the other options are not likely to become powder:

Aluminium: Aluminium is a metal with a malleable property. When hammered, it will flatten and deform but not shatter into a powder.

Magnesium: Similar to aluminium, magnesium is a metal with malleability. It will bend and change shape under hammering but not turn to dust.

Iron: Iron is another metal known for its strength and ductility. It won't crumble under hammering.

Carbon, on the other hand, can exist in various forms. One common form is graphite, which is quite brittle and will break down into a fine powder when struck with a hammer.