colours seen in soap bubbles are due to
Soap bubble When light shines onto a bubble it appears to change colour. Unlike those seen in a rainbow, which arise from differential refraction, the colours seen in a soap bubble arise from interference of light reflecting off the front and back surfaces of the thin soap film. Depending on the thickness of the film, different colours interfere constructively and destructively.
Aqua regia Aqua regia (/ˈreɪɡiə, ˈriːdʒiə/; from Latin, lit. "royal water" or "king's water") is a mixture of nitric acid and hydrochloric acid,[1] optimally in a molar ratio of 1:3. Aqua regia is a yellow-orange fuming liquid, so named by alchemists because it can dissolve the noble metals gold and platinum, though not all metals.