The amount of the major enantiomer in a solution which is 80% optically pure is:

Let the major enantiomer is (-) form. 80% optically puremeans the mixture contains 80% of (-) enantiomer and 20% isthe racemate [i,e, 10% (-) and l0% (+)].'. Total percentage of (-) form: 80 + 10 = 90%