Question

why Hgcl2 is colourless but HgI2 is red in colour?​

Answer 1

Mercuric chloride appears as an odorless white crystalline solid.

Answer 2

• Salts are formed as a combination of two or sometimes more than two elements.
• If not every time, often salts exhibit characteristics of their parent elements and are influenced in similar ways.
• Mercury Chloride is made of Mercury and possibly Hydrochloric acid which is a strong acid thus causing a reaction and rendering it colourless.
• Mercury Iodide on the other hand is made of Mercury and possibly an acid of Iodine which might not have reacted completely due to some molecular reasons thus resulting in a magenta reddish  shade.