Question

in a water molecule: covalent bonding (intramolecular) h-o-h
cross two or more water molecules: (intermolecular force) h₂o … h₂o … h₂o

• compounds with high intermolecular forces have high melting point, high boiling point and high viscosity.
• because of high intermolecular forces, water has a high boiling point (100 degree c) and high freezing point (0 degree c)

a. define allotropes : an element exists in different physical forms.
b. the different allotropes of carbon (c) are coal, graphite, diamond (is a hard substance, is used to cut glass)
and ______

Explanation:

The question (part b) is about the different allotropes of carbon. The known allotropes of carbon include coal, graphite, diamond, and another common one is buckminsterfullerene (or C₆₀). Since the sentence starts with "and", we need to provide the missing allotrope. The common allotropes of carbon are diamond, graphite, coal, and buckminsterfullerene (or C₆₀, or sometimes amorphous carbon is also considered, but buckminsterfullerene is a well - known allotrope).

Answer:

buckminsterfullerene (or C₆₀)