Given that t50 is 200seconds What is t75%

Plz choose one of the compounds from the table and explain how you know the numbers of atoms in your formula. is it possible for two different compounds to be made from the exact same two elements? why or why not? with a limited number of elements (less than 120 are known), does this mean we also have a small number of compounds or do we have a large number of compounds in this world?

Stage in which a typical star has completely stopped fusion

Calculate the percent composition by mass of each element in al(oh)3. use at least three significant figures.