Question

1. how was the sun formed?

when planets collided together\twhen nuclear fusion began in a collapsing cloud
when a nebula exploded\twhen gas froze into a solid

1. what process causes atoms to stick together and form larger objects?

fusion\taccretion\tevaporation\tmelting

1. what were planetesimals?

small stars forming near the sun\tobjects about a mile wide that formed planets
clouds of gas around planets\tpieces of planets blown away by wind

1. why are the inner planets rocky instead of gaseous?

they formed later than the outer planets\tthe sun’s wind blew their gases away
they are farther from the sun\tthey never had gas to begin with

Explanation:

1. The Sun formed from the gravitational collapse of a giant molecular cloud; as the cloud contracted, its core became dense and hot enough to ignite nuclear fusion, which marked the Sun's birth.
2. Accretion is the process where particles, atoms, or small objects stick together and accumulate to form larger celestial bodies.
3. Planetesimals are small, solid celestial objects that are the building blocks of planets, typically ranging in size from meters to kilometers (around a mile wide fits this description).
4. The young Sun's powerful solar wind was able to blow away the lighter gaseous materials from the inner regions of the solar system, leaving only denser rocky materials to form the inner planets.

Answer:

1. When nuclear fusion began in a collapsing cloud
2. Accretion
3. Objects about a mile wide that formed planets
4. The Sun's wind blew their gases away