Atoms of different isotopes of the same element differ in their total number of electrons neutrons protons valence electrons

Why does a plastic bottle that is sealed at a high altitude change it’s shape when taken to lower altitude

An ice cube with a volume of 45.0ml and a density of 0.9000g/cm3 floats in a liquid with a density of 1.36g/ml. what volume of the cube is submerged in the liquid

Which is an example of a highly unstable isotope that is often used in fission reactions?