The correct answer is: A. Hydraulic lime is generally obtained by burning kankar.
Hydraulic lime is a type of lime that sets and hardens under water. It is made by burning limestone that contains clay or other minerals. Kankar is a type of limestone that does not contain clay or other minerals. Therefore, hydraulic lime cannot be obtained by burning kankar.
B. Hydraulic lime sets slowly as compared to fat lime is a correct statement. Hydraulic lime sets slowly because it contains clay or other minerals that react with water to form a gel. Fat lime, on the other hand, does not contain these minerals and sets quickly.
C. Hydraulic lime is generally used in lime mortar is a correct statement. Lime mortar is a type of mortar that is made from lime, sand, and water. It is used to bind bricks and stones together. Hydraulic lime is a good choice for lime mortar because it sets and hardens under water.
D. None of these is not a correct statement. All of the statements are correct except for A.