Question

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

Answer 1

fats and oils are both of fatty acids. oils are generally liquid at room temperature due to unsaturated fatty acids .but fats are solid due to saturated fatty acids...

Answer 2

Butter is a source of animal fat, which is known for higher amounts of saturated fat. Mustard oil is a vegetable oil and contains more unsaturated fat.

Saturated fat has a higher melting point, that is a fact and the cause for the solid/liquid behavior of fats.