CBSE Class 10 Science 2020 · Paper 31(B) · Question 26

(a) Cinnabar is an ore of mercury; it is mercury sulphide, $\text{HgS}$. Mercury is low in the activity series, so it is extracted by heating alone. The enriched ore is heated in air (roasting), which converts it into mercuric oxide: $2\text{HgS}+3{\text{O}}_2\stackrel{\text{heat}}{\to }2\text{HgO}+2{\text{SO}}_2$. On further heating, the mercuric oxide is reduced to mercury: $2\text{HgO}\stackrel{\text{heat}}{\to }2\text{Hg}+{\text{O}}_2$. (b) An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. Advantages (any two): an alloy is harder and stronger than the pure metal (iron with a little carbon gives hard, strong steel); an alloy can have a lower melting point (solder, an alloy of lead and tin, is used for welding electrical wires); an alloy can resist corrosion better (stainless steel does not rust).