The correct answer is B.
Sensitivity is a measure of the change in strength of a soil when it is disturbed. It is defined as the ratio of the unconfined compressive strength of undisturbed soil to that of remolded soil.
Option A is incorrect because it is the percentage of volume change of soil under saturated condition.
Option C is incorrect because it is the ratio of volume of voids to volume of solids.
Option D is incorrect because it is not a valid option.