Cu ions plus EDTA2- ->cu(EDTA)2- plus 2H- number of moles of CU ions used which is equal to molarity multiplied by volume in litres that is 50xo.o2 divided by 1000 that is 0.001moles Since ratio is 1:1 the moles of EDTA is also0.001moles volume of EDTA is 0.001 divided by 0.0510m which is 0.0196 litres in ml is 0.0196x1000 which is 19.61ml
