Which law of planetary motion is responsible for?

None of Kepler's laws is responsible for the planetary orbits, in the sense that you mean. The laws are all consequences of Newton's law of gravity, so the planetary orbits are the result of gravity and inertia.

As soon as the nebula got thin enough -- as soon as nearly all the particles had condensed into lumps big enough -- so that friction was no longer a major force, then gravity determined all the rest.

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Yes, planets have orbits that are now pretty much set. But why is Earth at 1 AU from the sun, and not 0.8 AU or 1.2 AU? The answer to that is very complex, and has to do with the time when friction was an important force in the solar nebula.

Back in the early solar system, the orbits were not "set". Uranus and Neptune, for example, changed places. Jupiter formed much closer to the sun, and migrated outwards. Earth did not yet have the Moon. The solar nebula collapsed into the solar system about 4.6 billion years ago, but the orbits did not settle down until about 3.8 billion years ago.

Scientists did not understand this much until 7 years ago, and are still working on a lot of details.

I don't think there are any discrete orbits where planets necessarily form. It depends where the most matter collected and happened to form a dominant local gravitational influence.

To be honest, as an engineer I didn't study Kepler's Laws. They really aren't that important because they are just specific instances of Newton's Laws of motion and gravitation. All of Newton's Laws of motion and his Universal Law of Gravity together determine how matter behaves.