(A) (i) Give reasons for the following:

(I) Ionic compound have generally high melting points and boiling points.

(II) Solder, an alloy of lead and tin, is used for welding electrical wires.

(III) Carbon cannot reduce the oxides of Na or Mg.

(ii) The reaction of compound 'X' with aluminium is used to join railway tracks:

(I) Identify the compound 'X'.

(II) Name the reaction.

(III) Write the balanced chemical equation of the reaction of compound 'X' with aluminium.

OR

(B) (i) Write the balanced chemical equations when:

(I) A mixture of $Cu_2O$ and $Cu_2S$ is heated.

(II) $ZnS$ is heated in the presence of oxygen.

(ii) Give reasons for the following:

(I) The wires carrying current in homes have a coating of PVC.

(II) To make hot water tanks, copper is used and not steel.

(iii) Show the formation of ionic compound $CaO$ with electron dot structure. [Atomic number: $Ca = 20, O = 8$]

(A) (i) (I) Ionic compounds have high melting and boiling points because of the strong electrostatic forces of attraction between the oppositely charged ions. (II) Solder, an alloy of lead and tin, is used for welding electrical wires because it has a low melting point and is malleable. (III) Carbon cannot reduce the oxides of Na or Mg because these metals are more electropositive than carbon and their oxides are very stable. (ii) (I) The compound 'X' is thermite. (II) The reaction is thermite reaction. (III) $Fe_2O_3 + 2Al ightarrow 2Fe + Al_2O_3 + Heat$ OR (B) (i) (I) $2Cu_2O + Cu_2S ightarrow 6Cu + SO_2$ (II) $2ZnS + 3O_2 ightarrow 2ZnO + 2SO_2$ (ii) (I) The wires carrying current in homes have a coating of PVC because PVC is an insulator and prevents the flow of electric current. (II) Copper is used to make hot water tanks and not steel because copper is a good conductor of heat and steel is not. (iii) $\boxed{Ca ightarrow Ca^{2+} + 2e^-}$ $\boxed{O + 2e^- ightarrow O^{2-}}$ $\boxed{Ca^{2+} + O^{2-} ightarrow CaO}$