I can be solid, liquid, or gas, yet I am not a shape-shifter. My atomic number defines me, but I can change states. What am I?

Category: Science · Difficulty: hard

Hint: Think of the most essential compound for life.

Answer

Hydrogen (H2)

Explanation

Water can exist as ice (solid), liquid water, or vapor (gas) depending on temperature and pressure.

This is a hard science riddle — a tricky one that takes a little thought. The answer is Hydrogen (H2).

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