The density of medium A is more than medium B but less than medium C. In which medium does the sound travels fastest ?

The correct option is C.

Explanation:
Sound is a mechanical wave that requires a physical medium to travel. The speed of sound in a medium depends primarily on two properties of the medium: its elasticity (rigidity or bulk modulus) and its density.

Generally, for different states of matter or materials, mediums with higher density (such as solids compared to liquids or gases) also possess significantly higher elastic modulus (bulk modulus or Young's modulus). Because the increase in elasticity far outweighs the increase in density across denser mediums, sound travels fastest through denser mediums.

Given the densities of the mediums:
Density of Medium C > Density of Medium A > Density of Medium B

Since medium C is the densest among the three, sound will travel the fastest in medium C.