When you are dealing with mole calculations, whatever you do to one side of the equation you must also do to the other. .5Fe is 1/8th of 4Fe, so in order to determine what it will yield you must divide the given amount of Fe2O3 and divide THAT by 1/8th, leaving you with .25 mol of Fe2O3.
The answer to that is mass and chemical
The correct chemical formulae is CsBr
You can put a known amount sodium into some sort of time release mechanism such as a pill made from soluble material. Then you can place the sodium into a calorimeter with a known mass of water and record the temperature change the water undergoes during the reaction. Then you can use the equation q(water)=m(water)c(water)ΔT to find the amount of heat absorbed by the water. since the amount of heat absorbed by the water is the amount of heat released from the sodium, q(sodium)=-q(water). Than you can use the equation q(sodium)=m(sodium)c(sodium)ΔT and solve for c(sodium)
I hope this helps and feel free to ask about anything that was unclear in the comments.