Question

Is there any medium which reflects 100 percent of sound

Answer 1

may or may not, becoz it depends on the hardness of medium to reflect the amount of sound

Answer 2

A sound reducing barrier wall such as the LSE® 2000 with a porous surface material and sound-dampening content material is said to be absorptive. This means little or no noise is reflected back towards the source or elsewhere. Hard surfaces such as masonry or concrete are considered to be reflective.