Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: Mouth Brooding. Some species of fish carry their fertilized eggs in their mouth until they hatch. This is called mouth brooding. If you look closely, you can see the eggs inside the mouth of the cardinalfish pictured here. Answer: mouth brooding
[A]: Some species of fish carry their fertilized eggs in their mouth until they hatch; this is called what?

[Q]: Passage: Whales and bats have the trait of echolocation. This is the ability to locate objects in the dark by bouncing sound waves off them. The most recent common ancestor of whales and bats did not have this trait. Apply lesson concepts to explain how the trait evolved in whales and bats. Answer: echolocation
[A]: What term is defined as the ability to locate objects in the dark by bouncing sound waves off them.

[Q]: Passage: A: Any element in group 1 has just one valence electron. Examples include hydrogen (H), lithium (Li), and sodium (Na). Any element in group 18 has eight valence electrons (except for helium, which has a total of just two electrons). Examples include neon (Ne), argon (Ar), and krypton (Kr). Oxygen, like all the other elements in group 16, has six valence electrons. Answer: one
[A]:
How many valence electrons does a sodium atom have ?