if 1.0 L of a 2.0 M solution contains 1.204 * 10^24 molecules of a solute, how many molecules of solute will 1.0 L of a 0.5 M solution contain?

The formula for molariy is nomber of moles/volume

0.5=n/1=>n=0.5 moles

one mole contains 6.023*10^23 molecules

so 0.5 contain 3.0115*10^23 molecules

periodic trends is an atom that gets larger as the number of electronic shells increase, the radius of atoms increases as you go down a certain group in the periodic table of elements. in general, the size of an atom will decrease as you move from left to right of a certain period.