The myth among the options provided is:
Muscle tissue weighs more than fat.
This statement is misleading because a pound of muscle and a pound of fat both weigh the same (one pound). The confusion often arises from the fact that muscle is denser than fat, so a pound of muscle takes up less space than a pound of fat, but in terms of weight, they are equivalent.
The other statements, while they may vary in context or nuances, are generally accepted truths about exercise.