A zinc plate was kept in a glass container having `CuSO_(4)` solution. On examining it was found that the blue colour of the solution is getting lighter. After a few days, when the zinc palte was taken out of the solution, a number of small holes were noticed in it. state the reason and give chemical equation of the reaction invovled.

A solution of CuSO4 was kept in an iron pot. After few days the iron pot was found to have a number of holes in it. Explain the reason in terms of reactivity. Write the equation of the reaction involved.

A copper plate was dipped in AgNO_(3) solutions. After certain time, silver from the solution was deposited on the copper plate. State the reason whhy it happened. Give the chemical equation fo the reaction involved.

A solution of ferrous sulphate was kept in an aluminium can was found to have a number of holes in it. After few days, the can Explain the observation and write the chemical equation involved.

(i) Four samples A, B, C and D change the colour of pH paper or solution to Green, Reddish-pink, Blue and Orange. Their pH was recorded as 7, 2, 10.5 & 6 respectively. Which of the samples has the highest amount of Hydrogen ion concentration? Arrange the four samples in the decreasing order of their pH. (ii) Rahul found that the Plaster of Paris, which he stored in a container, has become very hard and lost its binding nature. What is the reason for this? Also, write a chemical equation to represent the reaction taking place (iii) Give any one use of Plaster of Paris other than for plastering or smoothening of walls.