Mendeleev left gaps in the periodic table because, in the future, he knew that there would be more elements to be discovered because not all elements were discovered at the time.
Hope this might help a little
Answer:
10.81, Boron
Explanation:
I love the explanation Khan Academy gives.
Answer:
Clouds are formed when water warms up and changes into a gas called water vapor, which rises up into the air.
Explanation:
Im pretty sure its D. I would wait for others though.