Polar covalent bonds (because hydrogen and oxygen form polar bonds and are both nonmetals so it's covalent) and hydrogen bonds (because the water molecules are attracted to each other with partial charges, causing specific properties like surface tension).
So in my very bad drawing that I attached in case you're more a visual learner, the d- and d+ show the partial charges of hydrogen and oxygen (making it polar, as the electrons in the bond are more shifted towards oxygen, which is why oxygen has a negative sign) and the yellow dotted line show the hydrogen bonds.
A isotope is atoms of the same element with different amount of neutrons to change the mass. They can become more stable by sharing or giving away electrons to have a stable electron shell
Magnesium sulfite is the magnesium salt of sulfurous acid with the formula MgSO 3. Its most common hydrated form has 6 water molecules making it a hexahydrate, MgSO 3·6H 2O.