Physical changes happen when you do/mix something that can be reversed. Best example is ripping a paper, you can just tape it back together so it is just an observable thing that changes, which is a physical change. Chemical changes happen when you mix things and they make a new substance and can’t be reversed. The best example of this is the Statue of Liberty, which changed in color due to the chemical change between the oxygen and copper, which created a new substance (rust) which made it green instead of copper.
Sorry for the long answer but hope this helps!
I THINK IT IS 16 BECAUSE THE ATOMIC NUMBER AND THE NUMBER OF PROTONS ARE THE SAME

Explanation:
the bottom number would be 54. This is because you add one to 53 to make it 54 and you add 0 to 138.
Attraction between a cation in one element and an anion in the other element
Answer:
A polar bond is one where the charge distribution between the two atoms in the bond is unequal. A polar molecule is one where the charge distribution around the molecule is not symmetric. It results from having polar bonds and also a molecular structure where the bond polarities do not cancel.
Explanation: