Susan has a beaker with one mole of water and another beaker filled with one mole of hydrogen chloride. Compare the number of molecules that Susan has of each
substance.

Ratio is 1:1 ; they have same number of molecules.

Explanation:

One mole of any compound have same number of molecules, irrespective of their chemistry and composition, i.e. 6.022x10^23 . This number is known as Avogadro's Number.

So the beaker with one mole of water contains = 6.022x10^23 molecules ;

and beaker with one mole of Hydrogen chloride = 6.022x10^23 molecules.

The comparative ratio is 1:1.

why do the isotopes of a particular element behave differently in nuclear reactions but the same in chemical reactions? chemical reactions involve changes to electrons in an atom; isotopes do not differ in electrons, and so they react the same way during chemical changes.