In this question the important concept to have in mind is: molar ratio. Molar ratio in a reaction is basically telling us how many moles I need of a compound in order to have a certain amount of moles as products, for example:
Let's say we have this reaction:
2 A + 3 B -> 2 C
The molar ratio for reactant A and product C is 2:2, which means I need 2 moles of A to end up with 2 moles of C.
In our question we have the equation already properly balanced, so what we need to do is just find these molar ratios
4. 3 moles of MnO2 we will get 2 moles of Al2O6, this is basically repeating the information from the balanced equation, therefore letter B
5. The molar ratio between Al and Al2O6 is 4:2, but we only have 2 Al, therefore we will only have 1 Al2O6, letter A
6. In this case we can build a calculation, molar ratio between MnO2 and Al2O6 is 3:2, but we want 3 Al2O6
3 MnO2 = 2 Al2O6
x MnO2 = 3 Al2O6
x = 4.5 moles or 4 1/2, letter C
