Question

nitric acid cannot be concentrated beyond 68% by the distillation of a dilute solution of HNO3. state the reason

Answer 1

One cannot concentrate nitric acid by distillation beyond 68% because Nitric acid is miscible with water in all proportions, forming hydrates at low temperature.

Since Nitric acid is not very easy to dilute so there is no way to separate HNO3 beyond 68% by distillation.