Is it true or false that if you are sitting still right now, the net force acting on you is zero?

Yes. Your weight is pulling you to center of the world. Weight is a force (gravity).
And since you're still on where you sit, the thing you're sitting on, exerts an equal force to your weight. That's stated in Isaac Newton's third law of motion. Simply 'For every action, there is an equal and opposite reaction.'

Newton's second law of motion looks so simple that we don't spend
too much time looking at it, and we don't realize how powerful it is.
Here's the law:

            Net force = (mass) x (acceleration).

To look at it in a slightly different way, divide each side by 'mass':

           Acceleration = (net force) / (mass) .

From this, we can see that if a thing is not accelerating,
then the net force on it must be zero.

If you are sitting still, then you are definitely not accelerating.
So the net force on you must be zero.

An atom that has fewer electrons that protons is called a positive ion.