Why are clouds white but rain clouds dark?

Answer: Rain clouds are thicker

Rain clouds are thicker ✓ — Correct! All clouds scatter sunlight, making them white. But rain clouds are much thicker and denser. As light passes through, most gets absorbed before reaching the bottom. Less light escapes, making them appear dark gray. The darker the cloud, the more water it holds, so rain is more likely!

Different cloud materials — Wrong. All clouds are made of water droplets or ice crystals. Rain clouds appear dark because they're thicker and denser, not because they're made of different materials.

Rain clouds cast shadows — Wrong. While rain clouds can cast shadows on the ground, their dark appearance is due to their thickness absorbing light as it passes through, not from shadows they create.