First you have to count all the atoms of each element in both sides of the reaction, in this case: Left side: there is one K atom, one Cl atom and 3 O atoms Right side: there is one K atom, one Cl atom and 2 O atoms
K and Cl are balanced but O isn't To balance O you can add a coefficient to O2 in the right side of the equation like this:
KCIO3 → KCI +3 O2
Now you have 6 oxygen atoms in the right side but only 3 in the left side, so you can add a coefficient to KClO3:
2KCIO3 → KCI +3 O2
And finally, Balance K and Cl again by adding a 2 as a coefficient for KCl
2KCIO3 → 2KCI +3 O2
Now both sides have the same amount of atoms of each element (2 K atoms, 2 Cl atoms and 6 O atoms)
I had to look for the options and here is my answer: The two requirements for nuclear fusion that are needed to be met in order for the elements hydrogen and helium fuse to make heavier elements are extremely high temperatures and density. Hope this helps.