There are 4 fundamental forces : gravity, elecgromagnetic, weak nuclear and strong nuclear.
The strong nuclear force acts between nucleons (neutrons and protons).
Between 0.5fm and 3fm it is attractive, at seperations smaller than this its repulsive. Its used to overcome electrostatic repulsion in atoms to hold the atoms together (coz you have protons in a nucleus and they repel each other, so some force must be there to keep the atom together: that force is called the strong nuclear force.
As I said, SNF only works between nucleons, so it can act on hadrons. But a lepton is a fundamental particle and is not a nucleon (proton or neutron) so it does not interact between them.
I can't remember the answers to your other questions, but if you're doing aqa I don't think you have to know why, you just need to know the facts, but check spec to be sure. Still good to try and find out tho.