The correct option is
C 21
Water resources comprising of surface water (river and lakes), ground water, marine and coastal waters, support all living things including human beings.
Basically, man requires safe protected water supply for drinking, cooking, washing, and bathing. Underground water is also used for the purpose of irrigation and other utilities.
All industries require water either for processing or for other utilities.
In Tamil Nadu, there are around 21 major lakes in Tamil Nadu, named as below:
Adambakkam Lake,
Avalanche Lake (Ooty, Tamil Nadu, India),
Chetput Lake,
Chitlapakkam Lake,
Kaliveli Lake,
Kolavai Lake,
Korattur Lake,
Madhavaram Lake,
Maduranthakam lake,
Mangal Lake (Chennai),
Mathiyampatti Lake,
Mookaneri Lake,
Pallavaram Lake,
Parakkai Lake,
Perumal Eri,
Porur Lake,
Pulicat Lake,
Retteri,
Tiruninravur Lake,
Velachery Lake,
Lake Vennandur and
Villivakkam lake
Hence, the correct answer is 21.