CBSE Class 10 Science 2019 · Paper 31/1/2 · Question 17

(a) (i) $\text{Ca}+2{\text{H}}_2\text{O}⟶{\text{Ca(OH)}}_2+{\text{H}}_2$ (ii) $2\text{HgS}+3{\text{O}}_2\stackrel{\text{heat}}{\to }2\text{HgO}+2{\text{SO}}_2$ (on further heating, $2\text{HgO}\stackrel{\text{heat}}{\to }2\text{Hg}+{\text{O}}_2$) (iii) $3{\text{MnO}}_2+4\text{Al}⟶3\text{Mn}+2{\text{Al}}_2{\text{O}}_3+\text{heat}$ (b) An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal. Two properties: alloys are harder and stronger than the pure metals, and they resist corrosion better. (They also have lower melting points and lower electrical conductivity; any two properties are accepted.)