Study the diagram given below and answer the questions that follow :

What is the value of X?
Topic: Formation of uranium-236
Answer
From the diagram, a uranium-235 nucleus absorbs a neutron before it undergoes fission.
₉₂U²³⁵ + ₀n¹ ⟶ ₉₂U^X
Mass numbers must balance on both sides: 235 + 1 = X X = 236
Value of X = 236
In any nuclear equation the mass numbers must balance and the atomic numbers must balance, separately. Here the neutron adds 1 to the mass number and 0 to the atomic number, so uranium-235 becomes uranium-236 — the same element, one unit heavier.
Uranium-236 is the unstable intermediate that then splits. That is why the nucleus has to capture the neutron first: U-235 on its own is relatively stable, and it is the added neutron that tips it over into fission.