Which protein functions as a motor protein that applies the power stroke during muscle contraction?

Myosin

Explanation:

Myosin is an ATPase protein that moves along actin and, in presence of ATP, are responsible for muscle contraction. These proteins are the main components of myofilaments, the organelles that make up the "skeleton" of muscle cells. The myosin makes up the thick filaments and is classified as a mechanochemical enzyme or motor protein, because it is able to convert chemical energy into mechanical energy, useful for the mechanism of muscle contraction.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.