Select the word or phrase from the drop-down menu to describe ionic compounds. A formula unit represents the simplest ratio of elements in a of an ionic compound. A crystal is made up of There are two magnesium ions for every two sulfide ions in magnesium sulfide. The ratio of Mg to S in the formula unit is

c is the answer because when something is left after something evaporates that shows the chemical change.

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.