How do you measure mass and density? Does greater mass imply greater density? What quantity determines floating or sinking? Is it true to say that light objects float and heavy objects sink?

What is Archimedes principle? What is it good for?

What is the law of definite proportions?

What do elements in the same column of the Periodic Table have in common?

What buildup principle puts elements on the same row in the Periodic Table?

What is meant by "main group" elements?