(1) From Figure A, we know that the gravity of the object is G=10N. From Figure C, we can see that the tensile force F of the spring dynamometer in kerosene is 7.6N,
Therefore, the buoyancy force F on the metal block in kerosene = G-F pull = 10N-7.6N = 2.4N
So the answer is: 2.4.
(2) Looking at the relationship between the buoyancy and the density of the liquid, it should be ensured that when other physical quantities remain unchanged, only changes in density cause buoyancy changes. Therefore, two groups of experiments B and C should be selected for research.
So the answers are: B and C.