What are colliding when plateaus and mountains ranges are formed

mountain ranges form when pieces of Earth's crust—called plates—smash against each other in a process called plate tectonics, and buckle up like the hood of a car in a head-on collision.

Hope that answers your question.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).

there are two significant figures.