No. A nebula is generally much larger than a solar system. We believe that our sun and solar system came to be when a nebula collapsed under the influence of gravity, and the gas of the nebula became the Sun and our planets - and everything else.
Most of the mass in the solar system is contained in the Sun. The sun makes up 99.85% of the total mass.
Our own sun attracted the material that eventually became he solar system. However since the wide range of materials present (all the elements) required the interaction of may suns to form an reform the atoms there are a myriad of unknown older stars represented in the solar system
The inner planets
The percentage of uranium on all the planets in our solar system is almost certainly identical as it all came from the same source in supernovas that predated the formation of the nebula that became the solar system.
Many. In the early solar system, there were many more planets than there are now. Most hit joined into larger planets and a few were captured and became moons.
"Our solar system." The "part of our galaxy" that's in our solar system is the solar system.
Our Solar System is called the Solar System, Why?, what do you Aliens call it.
No. There is one star in our solar system, and no other solar systems within it.
The solar system
There are no exoplanets in our solar system. By definition, an exoplanet is a planet that is not in our solar system.