How to calculate the mass ratio of zinc to iodine in zinc iodide ?

The mass ratio of zinc to iodine is 1 to 3.882.

The mass ratio of two in a compound is the mass of one element in a given amount of the compound divided by the mass of the other element.

Let's calculate the mass of ##"Zn"## in 1 mol ##"ZnI"_2##.

##"Mass of Zn" = 1 color(red)(cancel(color(black)("mol ZnI"_2))) × (1 color(red)(cancel(color(black)("mol Zn"))))/(1 color(red)(cancel(color(black)("mol ZnI"_2)))) × (65.38 "g Zn")/(1 color(red)(cancel(color(black)("mol Zn")))) = "65.38 g Zn"##

Also, the mass of ##"I"## in 1 mol of ##"ZnI"_2## is

##"Mass of I" = 1 color(red)(cancel(color(black)("mol ZnI"_2))) × (2 color(red)(cancel(color(black)("mol I"))))/(1 color(red)(cancel(color(black)("mol ZnI"_2)))) × (126.9 "g I")/(1 color(red)(cancel(color(black)("mol I")))) = "253.8 g I"##

∴##"Mass of Zn"/"Mass of I" = "65.38 g"/"253.8 g"##

To get the ratio in its smallest terms, we divide the numerator and the denominator by the smaller number (##"65.38 g")##.

Then

##"Mass of Zn"/"Mass of I" = 1/3.882##