The process of photosynthesis starts when the sunlight strikes the photosystem I pigments which excites these electrons. This energy is passed from molecule to molecule until it reaches the chloroplast molecule which is called P700. This molecule is so named since it only absorbs the light in the red region of the spectrum that has the wavelength of 700 nanometers. The photosynthesis process starts at this point where the chlorophyll pigment absorbs the sunlight and begins the process of converting this light to energy.
Hence the option that states that pigment molecules absorbs the light energy begins the process of photosynthesis.
