Chromium (element)
鉻 centers on the metallic element chromium. It is a specialized character used for this chemical element, with no broader conceptual cluster.
鉻 combines 金 (metal) with 各, which likely contributes the sound. It was created as a character for chromium, a metallic element.
The left side 金 means metal, and the right side 各 looks like a container. Picture a shiny metal container holding pure chromium.
For ラク, imagine a rack of chromium-plated tools: rack -> ラク, and the metal 金 shines on the rack.