CBSE Class 10 Science 2019 · Paper 31/1/1 · Question 16

(a) Three chemical properties that distinguish a metal from a non-metal (the table is set out in step 5): Reaction with oxygen: a metal forms a basic oxide, for example $\text{MgO}$; a non-metal forms an acidic or a neutral oxide, for example ${\text{SO}}_2$ or $\text{CO}$. Reaction with dilute acids: a metal such as zinc displaces hydrogen from dilute acids; a non-metal does not displace hydrogen from dilute acids. Ions formed: a metal forms positive ions by losing electrons, for example ${\text{Na}}^{+}$; a non-metal forms negative ions by gaining electrons, for example ${\text{Cl}}^{-}$. (b) (i) Metals have free electrons: the outer electrons of metal atoms are loosely held and easily lost, so they move freely through the metal and carry the electric current. (ii) Aluminium is more reactive than iron, so it displaces iron from iron(III) oxide: ${\text{Fe}}_2{\text{O}}_3+2\text{Al}\to 2\text{Fe}+{\text{Al}}_2{\text{O}}_3+\text{heat}$. The reaction is so highly exothermic that the iron formed is molten; the molten iron fills the crack between the machine parts and joins them when it solidifies (thermit welding).