Correct Answer: Sterile

Solution : The correct choice is the third option .

Impure means something that is adulterated and mixed with some foreign matter.

Sterile means free from bacteria. Both of the words imply opposite things, as one means to be adulterated, whereas the other implies something that is free from any foreign matter, thus making them antonyms

The meanings of the other options are as follows:

• Contaminated means something that is less pure.
• Segregated means something that is set apart from each other.
• Concentrated means rich in respect to a particular element.