Why do comets have tails?

Answer: Solar wind and heat create them

Solar wind and heat create them ✓ — Correct! Comets are 'dirty snowballs' made of ice, dust, and rock. Far from the Sun, they're frozen and tailless. When they approach the Sun, solar heat vaporizes the ice, releasing gas and dust. Solar radiation pushes dust particles away, creating a yellowish dust tail. Solar wind (charged particles) blows gas away, creating a blue ion tail. Both tails always point away from the Sun, not behind the comet's motion. As the comet moves away from the Sun, it freezes again and the tail disappears.

They leave debris behind — Wrong. Comets do leave some debris along their orbits (causing meteor showers when Earth passes through), but this scattered debris isn't what we see as the comet's tail. The visible tail is gas and dust actively being blown away from the comet by solar wind and radiation, forming streams that point away from the Sun.

Gravity pulls material out — Wrong. Gravity doesn't pull material out to form tails - gravity would pull material inward, not outward. The tails form because solar radiation pressure and solar wind (stream of charged particles from the Sun) push gas and dust away from the comet, creating tails that point away from the Sun.