The Activa is a popular scooter manufactured by Honda. The Activa's fuel efficiency depends on several factors such as road conditions, riding style, load, and maintenance. While the Activa has a decent fuel tank capacity, it's unlikely that you'll be able to cover 300 km without making any stops for refueling.
The Activa typically has a fuel tank capacity of around 5 to 6 liters. The actual mileage you can achieve will vary, but it's generally in the range of 40 to 50 km per liter. Considering the higher end of the mileage range, if your Activa achieves 50 km per liter, a full tank of 6 liters would allow you to cover approximately 300 km.
It's always a good idea to keep an eye on your fuel gauge and plan for refueling stops accordingly to avoid running out of fuel during your journey.