Mr. Knowlton loves to throw a football around for fun. In the summer, he and his brothers bought a new ball that was in perfect
condition. However, in the winter they noticed that the ball was not
the same. It seemed to have less volume even though there were no
leaks in the ball! Why?

If a hydrogen atom is neutral, it must also have  one electron. an oxygen atom (o) has an atomic number of eight (8). this means a neutral oxygen atom has eight protons and eight electrons. the element actium (ac) has an atomic number of 89, so it has 89 protons and 89 electrons in a neutral atom

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