Which of these are broken down during chemical, but not physical changes?
I am not so sure about this one... sorry
According to the periodic table of the elements, which set of elements has similar properties?
He, Ne, Ar have similar properties because there in the same group.
What is its mass number?
Beryllium's mass number is 9.
I am so sorry I wasn't able to answer the 1st question... but I hope I helped you.