Density (though they are not all the same)
The word 'planet' is a common noun, a word for any planet. A proper noun, for example 'Jupiter', is the name of a specific planet.
So far every planet has an atmosphere... i think.
'Hemisphere' means 'half a sphere' So every sphere has two halves. So every planet has two hemispheres. You can divide the planet into hemispheres any way you like. It's common to talk of the northern hemisphere and the southern hemisphere, or the eastern and western hemispheres, but if you want to suggest your own hemispheres then that's your choice.
NO, because it is not possible. Every plutoid is a dwarf planet but every dwarf planet is not a plutoid.
YES, obviously, because every plutoid is a dwarf planet but every dwarf planet is not a plutoid.
No, "planet" is a common noun.
Humans are the dominant species on the planet Earth. You will find them, or proof of their existent in every habitat, every continent, every landmass on the planet.
What is the average tempurature for every planet in the solar system?
In this context, it is common. As the name of a restaurant, like Planet Hollywood, it's proper.
Yes, planetary systems are common in the universe. Nearly every star observed so far has been found to have at least one planet orbiting around it, suggesting that planetary systems are a common feature in the galaxy.
Pretty much every planet has an axis, because an axis is what a planet rotates around. Any planet that rotates has an axis, and pretty much every planet known rotates.
yes