[5] Q4 a) Explain the process curing of concrete? Explain the significance of this process and what are its purposes? b) A silicon wafer (n=1.388x1016 atoms / m) is doped with 4.50 x 10" boron atoms/mat 27C. The mobilities of electron and hole are 0.35 m /V.s and 0.68 m/ V.s respectively. Calculate the electrical resistivity of the material before and after the addition of boron atoms? c) Justify the following statement with valid reasoning. The most environmentally aware people condemn the use of plastics. Total 25 Marks [10] [10]