Assertion (A): When the surface of a lake is cooled during winter, the cooled surface water descends to the bottom as long as its temperature exceeds 4OC, but when cooled below 4OC, it floats at the top.
Reason (R): Ice forms at the top of a pond in winter while bottom fluid stays warmer at more than 4OC.
a. Both A and R are individually true and R is the correct explanation of A.
b. Both A and R are individually true but R is not the correct explanation of A.
c. A is true but R is false
d. A is false but R is true