Which of the following best explains why diamonds are very hard?
a. diamonds are made up of several different isotopes of carbon.
b. diamonds are made up of several different allotropes of carbon.
c. the atoms in a diamond are arranged in a rigid crystalline structure.
d. the atoms in a diamond are arranged in flat sheets that are tightly bonded.

Option (C)

Explanation: Diamond is the hardest element and it is because the carbon atoms are linked with one another by a strong covalent bond, forming an unbreakable crystalline structure. Covalent bonds are formed when atoms share electrons with each other.

According to the Mohr's hardness scale, diamond has hardness of 10, being the hardest of all. It is denoted by C and it crystallizes in the isometric system and its durability is very high.

Diamonds are found in the kimberlite pipes, where the kimberlite rocks are located at a great depth having extreme pressure condition.

Diamonds are often used in the jewelries.

Thus, the correct answer is option (C).

the old alchemists made significant contributions to science even though there starting premises were off a bit. their conclusions after failure would steer them into better directions for investigation. science is no more than close observation and the initial mistakes result in rethinking and retrying experiments.