Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

You call egg-shaped galaxies, which are reddish to yellowish in color because they contain mostly old stars, elliptical galaxies.
What do you call egg-shaped galaxies, which are reddish to yellowish in color because they contain mostly old stars?

Salt-water biomes in the ocean are called marine biomes.
Salt-water biomes in the ocean are called what?

The octet rule is a result of trends in energies and is useful in explaining why atoms form the ions that they do.

Which rule is a result of trends in energies and is useful in explaining why atoms form the ions that they do?