They are the hydrogen and oxygen of the water itself. After that it's chlorine and sodium.
hydrogen and oxygen
sodium and chlorine
You think probable to sodium chloride (NaCl).
You think probable to sodium chloride (NaCl).
You think probable to sodium chloride (NaCl).
These elements are transported by rivers to the sea. Another source is the volcanic activity.
potassium and sulfate
Basically all of them. However, most stars contain large amounts of hydrogen (since that's the most common element in the Universe), as well as helium, as well as smaller amounts of other elements.
Hydrogen is not made up of any other elements but hydrogen. The hydrogen atom has 1 proton, 1 electron, and the most common isotope has no neutrons. The other two uncommon isotopes have one or two neutrons.
Chlorides salts of Na, Mg, Ca.
Sodium chloride, potassium chloride, magnesium chloride
The two most common elements in the Universe, and in most stars are - in that order - hydrogen and helium (elements #1 and #2).
Helium and Neon are considered the two most inert elements.