[2 marks] a) What do you understand by the term leaching [3 marks] b) Describe how equilibrium can be attained in solid-liquid extraction 3 c) 100 kg solids containing 18 per cent of extractable matter of density 2700 kg/m' are fed to a plant for washing in a counter-current manner and which requires 200 volumes of liquid/100 volumes of solid for it to be capable of being pumped to the next stage. The strong solution is to have a concentration of 100 kg/m. If 98 per cent extraction of a material is to be achieved; i) Determine the ratio of the solvent discharged in the overflow to solvent discharged in the underflow [8 marks] ii) Calculate the number of stages required [7 marks]