Among the following , which is smallest . muscle fiber, thick filament , or myofibril ? which is largest ?

Fiber>Fibril>Fila: Bundles of protein filaments create a myofibril, and many myofibrils comprise the contracting bundles within a muscle fiber, which is an elongated, contractile, cell. In the picture nearby, the smallest unit shown is a muscle fiber, i.e. One cell --exagerrated in crossesectional size, of course. So the myofibrils within cannot be seen, nor the filaments of they are composed.

Muscle fibers: Largest is muscle fibers, then myofibrils then thin (actin) & thick (myocin) filaments as smallest.

Long answer: "muscle fiber" is the colloquial name for muscle cell, or myocyte, which is thus the largest unit. Myocytes in turn contain myofibrils, which contain thick filaments, composed of myosin. These units are all striated, or skeletal muscle.