The answer is wavelength. It is the distance between corresponding points of two consecutive waves (corresponding points are particles or points in the same phase, meaning the points have completed identical fractions of their periodic motion. In a transverse wave it is the distance between two successful crests or troughs while in a longitudinal wave is the distance between two successful compressions or rarefactions.
A compound forms whenever two or more atoms form chemical bonds with each other. The chemical formula for water is H2O, which means each molecule of water consists of one oxygen atom chemically bonded to two hydrogen atoms. Thus, water is a compound.
