187) When copper pyrites are roasted in excess of air, a mixture of CuO + FeO is formed. FeO is present as impurities. This can be removed as slag during reduction of CuO. The flux added to form slag is:

188) The phenomenon of removing layers of basic oxides from metals before electroplating is called:

189) The process of zone refining is used for:

190) Tin and lead are refined by:

191) Which of the following processes is used in the extractive metallurgy of magnesium?