Why is pure acetic acid often called glacial acetic acid?
(a) because it freezes just below 0°c, forming white crystals.
(b) because it freezes just below 100°c, forming white crystals.
(c) because it freezes just below room temperature, forming white crystals.
(d) because it freezes just above room temperature, forming white crystals.

The correct option is: (C) Because it freezes just below room temperature, forming white crystals

Explanation:

Acetic acid or ethanoic acid, is colorless liquid with a characteristic pungent smell and sour taste.  

In the pure form, acetic acid is known as glacial acetic acid. This is because it forms white crystals at 16.6 °C, i.e. just below the room temperature.

Since, glacial acetic acid is free of water molecules, it is also known as anhydrous acetic acid.