CBSE Class 10 Science 2018 · Paper 31/1/C · Question 16

(a) Metals versus non-metals (chemical properties): 1. Nature of oxides: Metals form basic oxides, e.g. $\text{MgO}$ (a few, such as ${\text{Al}}_2{\text{O}}_3$ and $\text{ZnO}$, are amphoteric); non-metals form acidic oxides, e.g. ${\text{SO}}_2$ and ${\text{CO}}_2$, or neutral oxides, e.g. $\text{CO}$. 2. Reaction with dilute acids: Metals above hydrogen in the activity series displace hydrogen from dilute acids, e.g. $\text{Zn}+2\text{HCl}\to {\text{ZnCl}}_2+{\text{H}}_2$; non-metals do not displace hydrogen from dilute acids. 3. Ions formed: Metals lose electrons to form positive ions (they are electropositive), e.g. $\text{Na}\to {\text{Na}}^{+}+e^{-}$; non-metals gain electrons to form negative ions (they are electronegative), e.g. $\text{Cl}+e^{-}\to {\text{Cl}}^{-}$. Other correct chemical properties, such as ionic chlorides of metals against covalent chlorides of non-metals, also earn credit. (b) Rusting of iron can be prevented by: 1. painting, oiling or greasing the iron, which keeps air and moisture away from its surface; 2. galvanising, i.e. coating the iron with a thin layer of zinc. Chrome plating, tin plating or making alloys such as stainless steel also prevent rusting.