An old, unpainted steel swing set in a park has developed a reddish-brown, flaky coating and is no longer considered safe. This is because the steel, which is mostly iron, has...

been physically weathered by wind and rain until it became smaller.

undergone a chemical reaction to form a weaker material.

absorbed water, making it heavier and less stable.

melted in the sun and re-solidified into a more brittle form.

A city's old iron water pipes are failing due to rust. What is the most likely chemical reason for this infrastructure failure?

The iron atoms in the pipes simply wore out and disappeared over time.

The water pressure physically bent the pipes until they became brittle.

The iron reacted to form a new, structurally weaker substance, iron oxide.

The pipes expanded and contracted with temperature changes, causing cracks.

Iron oxide is stronger and more flexible.

Iron oxide is weaker and more brittle.

Both substances have identical strength and structure.

Iron oxide is a liquid, while iron is a solid.

They are destroyed and replaced by new rust atoms.

They bond with other atoms to form a new compound.

They change their physical state from a solid to a powder.

They are washed away, leaving the weaker material behind.