<u>Answer:</u> The isotopic symbol of barium is
and that of strontium is 
<u>Explanation:</u>
Nuclear fission reactions are defined as the reactions in which a heavier nuclei breaks down in two or more smaller nuclei.
In a nuclear reaction, the total mass and total atomic number remains the same.
- For the given fission reaction:

Total mass on reactant side = total mass on product side
235 + 1 = A + 94 + 3
A = 139
Total atomic number on reactant side = total atomic number on product side
92 + 0 = Z + 36 + 0
Z = 56
The isotopic symbol of barium is 
- For the given fission reaction:

Total mass on reactant side = total mass on product side
235 + 1 = A + 143 + 3
A = 90
Total atomic number on reactant side = total atomic number on product side
92 + 0 = Z + 54 + 0
Z = 38
The isotopic symbol of strontium is 
Hence, the isotopic symbol of barium is
and that of strontium is 
There are a couple of ways todetermine if a reaction is exothermic or endothermic. Endothermic meaning that heat is added to the reaction to make the reactants interact and exothermic meaning heat is released during the reaction between the two reactants.
In endothermic reactions you can find a triangle above the arrow.
The balanced chemical reaction is :

Number of moles of Na,
.
Now, from balance chemical reaction we can see that 1 mole of oxygen reacts with 4 moles of sodium.
So, number of moles of oxygen are :

So, amount of oxygen required is :

Therefore, 5.08 gram of oxygen will react with 14.6 gram of sodium.