Question

why is butter solid and mustard oil liquid at room temperature?

Answer 1

This is why butter or ghee is solid at room temperatures, but olive or cotton oils are liquid. It is, in fact, the main distinguishing point between fats and oils. Coconut oil freezes at a higher temperature than mustard oilbecause it's a more saturated fat.

Answer 2

Everything has its own melting/boiling point