green, chlorine
綠 centers on the color green, often associated with plants and nature. The chlorine sense is a specialized modern chemical usage derived from the greenish color of chlorine gas.
綠 is the traditional form of modern 緑. It combines 糸 (thread) with 彔, which likely contributes the sound and may relate to the color of green plants or dyeing. The modern simplified form 緑 replaces 彔 with 录.
Picture green silk thread (糸) being dyed with a special green pigment extracted from the 彔 component, which looks like a plant with hanging fibers. The whole character 綠 is the color of that green thread.
For リョク, imagine a green cloak (リョク sounds like 'ryoku', close to 'cloak') made of green silk. The green cloak -> リョク, and it's the color of the thread in 綠.