The best answer is the isotope of strontium which is strontium-85. It has a half-life of about 64 days. The metal strontioum has four stable, naturally occurring isotopes which includes 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.0%) and 88Sr (82.58%).
In order to determine the mole ratio, you need to begin with a balanced chemical equation.
The answer you are looking for is "bromine". Hope this helps!
