Krypton-84 is the most abundant type of Krypton. The answer is C.
If you need this to be explained, I will do my best it's a bit difficult to say how to find it out, but I will if you need me to.
The answer to this question is 5
An element is a form of matter that is made of only one type of atom
M=mol/L, 0.323M=mol/0.01325. Rework to solve for mol and bam! (I.e. times the two numbers)