An ionic compound forms when Ca (Z=20) reacts with I (Z=53). A sample has 1.3x10^19 Ca ions, how many I ions?

Question

An ionic compound forms when calcium (Z = 20) reacts with iodine (Z = 53). If a sample of the compound contains 1.3 multiplied by 10^19 calcium ions, how many iodide ions does it contain?

Answer 1

with a formula CaI2

if there are

1.3 e19 Ca+2  => twice => 2.6e19 I- 's

your answer is: 2.6 e 19 iodides  (aka 2.6 multiplied by 10^19)

Answer 2

Most common compound formed is CaI2, so its twice as many.