A compound is where two or more elements have chemically bonded, and a mixture is where there are two or more elements are grouped together, but they are not chemically bonded.
An example of a mixture would be salt dissolved in water, and an example of a compound would be water (which is made up of 2 Hydrogen and 1 Oxygen bonded together)
tl;dr: I would go with B, basically.
Well, all of this we owe it to Bohr who analyzed the atomic emission spectrum of hydrogen and he could probe matematically that it was a result of movement of e- from an especific energy level to a lower one. The understanding of levels of energy took to the development of the atomic theory
0.912 mol Na2CO3 × 105.9888g Na2CO3/ 1 mol Na2CO3 = 96.66 grams