Answer:
Correct Option is (a).
Step-by-step explanation:
Order of increasing hardness is
Most plastics < cutting tools < brass < diamond
Diamond is the hardest from all above.
Diamond is formed from carbon atoms only and each carbon atom is attached to 4 other carbon atoms in tetrahedral geometry due to which it has a highly compact structure.
Brass is basically an alloy of two metals copper and zinc.
It is harder than its constituent metals but softer than diamond.
Plastics are least hard from the given options.