Why aluminium sheets do not corrode easily? Why does a copper vessel get covered with a green coating in the rainy season? 

You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute $\mathrm{HCl}$, dilute ${\mathrm{HNO}}_3$, ${\mathrm{ZnCl}}_2$ and ${\mathrm{H}}_2\mathrm{O}$. In which of the above containers these solutions can be kept? 

Explain the following term: 

 Precipitation reaction. 

Translate the following statement into chemical equation and then balance it. 

Carbon disulphide burns in air to give carbon dioxide and sulphur dioxide. 

Translate the following statement into a chemical equation and then balance it. 

Barium chloride reacts with aluminium sulphate to give aluminium chloride and a white precipitate of barium sulphate. 

Which of the following is not a physical change?  

Three beakers labelled as A, B and C each containing $25 \mathrm{ml}$, water were taken. A small amount of $\mathrm{NaOH}$, anhydrous ${\mathrm{CuSO}}_4$ and $\mathrm{NaCl}$ were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas, in the case of beaker C, the temperature of the solution falls. Which one of the following statements(s) is (are) correct? 

(i) In beakers A and B, an exothermic process has occurred. 

(ii) In beakers A and B, an endothermic process has occurred. 

(iii) In beaker C exothermic process has occurred. 

(iv) In beaker C endothermic process has occurred. 

A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?