What is generally said is that only 10% of energy gets retained at transfer, which means that 90 % is lost - this is the correct answer. The "loss" of energy mostly means that the energy gets transformed into heat (since we know that in any system no energy can be lost - this energy has to go somewhere, according to the laws of physics. ) and because not all energy can be absorbed (for example not all tissues are digested by the predator)
