ANS:A - Arsenides of heavy metals.

Speisses is a mixture of arsenides and antimonides of heavy metals. Speisses (or speiss) is a byproduct of smelting operations, particularly in the extraction of metals such as lead, copper, and nickel. It is often composed of various arsenides and antimonides of heavy metals, which are impurities that accumulate during the smelting process. These compounds can include arsenic, antimony, and other heavy metals such as lead, copper, or nickel. Therefore, the correct option is: Arsenides & antimonides of heavy metals.