Is a left out potato soup over night with lid on still safe to eat?

It's not recommended to leave potato soup out overnight, even with a lid on. Here's why:

* Bacteria growth: Even with a lid, bacteria can still grow in the soup, especially at room temperature. This can lead to food poisoning.

* Spoilage: The soup can start to spoil and develop an off-taste or smell.

To be safe:

* Refrigerate the soup within 2 hours of making it. This slows down bacterial growth.

* Store the soup in a sealed container.

* Eat the soup within 3-4 days.

If you're unsure, it's always better to err on the side of caution and throw it out.