Scientists used to believe that chemical reactions fueled the sun. Why did this lead them to believe that the sun was very young? Please explain in at least 2 sentences. Will give brainliest.

Yes she is correct. the answer is completely correct

☆ionisation energy increases across a period from na -> ar☆ionisation energy decreases down a group from li -> fr☆ionic radius decreases across a period from na -> cl☆ionic radius increases down a groupfrom f -> ii hope it clarifies your doubts

Not a  mixture of two common elements that can be separated by physical means.