Which of the following is true about elements and compounds?

Question: Which of the following is true about elements and compounds?

(a)they  contain to or more elements in a fixed ratio to each other(b) 25 compounds are essential to life(3) they are held Together by hydrogen bonds (4)all of the above answer: they contain two or more elements in a fixed ratio to each other element are the simplest  complete chemical  substance.  each element corresponds to a single entry on the periodic table.and element is a metallic that consist of a single type of atom is atom type contain the same number of proton compounds substance made up of more kind of atom compound can be broken down into simpler substance by chemical method property of a compound differs from the the that of their elements example: water NaCl and element are compounds are pure substance.