Explanation:

1. Asteroids are rocky debris of varying size orbiting the sun: This is correct. Asteroids are rocky bodies that orbit the Sun, and they vary widely in size.
2. Most of the asteroids are small but some have diameter as large as 1000km: This is also correct. While most asteroids are very small, there are some that are quite large. The largest asteroid, Ceres, has a diameter of about 940 kilometers, and it's so big that it's also classified as a dwarf planet.
3. The orbit of asteroids lies between the orbits of Jupiter and Saturn: This statement is incorrect. Most asteroids in our Solar System are found in the asteroid belt, which is located between the orbits of Mars and Jupiter, not between Jupiter and Saturn.