From identifying the elements that make up a star, astronomers can determine the star’s what?

Working out a star's age. Spectroscopy also tells us the age of a star by looking at the amount of its matter made up of chemical elements other than hydrogen and helium. "The earliest stars were composed of just hydrogen and helium because they were the first elements to form after the Big Bang".

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.

the ratio of the conjugate base to the acid required to attain the desired ph.