Hey there!
We know that a chemical reaction is balanced when there is the same amount of each element on both sides of the equation.
According to the law of conservation of mass, matter cannot be created or destroyed, so we must have the same amount of each element on each side of a chemical equation.
We count the amount of each element on each side, and the products should have the same number as the reactants.
Hope this helps!
Remark
The given thing on the right is a positron. The mass for these subatomic particles is considered to be 0. It's atomic number is 1 which means it is a blood relative of a proton.
So essentially what happens is that X is one space to the left on the periodic table. But let's solve this a little bit more formally.
Solution

y stays the same at 147. It is z that changes.
65 = z + 1 Subtract 1 from both sides.
64 = z
So the chemical with 64 as its position on the periodic table is
Gadolinium and the answer is C
Answer:
Resonance Structures for SCN-:[S-C N]-
Resonance StructureEnergy (kJ/mol)[S-C N]--23.00[S=C=N]