Final answer:
According to the Nebular Theory, planets form through the process of accretion. The solar nebula collapsed and solid particles condensed and coalesced into planetesimals, which collided and merged to form planets.
Step-by-step explanation:
According to the Nebular Theory, planets form through the process of accretion. The theory suggests that a rotating cloud of gas and dust called the solar nebula collapsed under its own gravity. As the nebula contracted, it flattened into a disk and solid particles began to condense and coalesce into planetesimals. These planetesimals then collided and merged, gradually accumulating mass and forming the planets.