Uranium-238 undergoes radioactive decay according to the incomplete below. 238 92
U= 4
2 He + X.
What is the decay product represented by X?

The decay product represented by X : Thorium (Th) : ²³⁴₉₀Th

Given

Decay reaction

²³⁸₉₂U ⇒ ⁴₂He + X

Required

The decay product

Solution

Radioactivity is the process of unstable isotopes to stable isotopes by decay, by emitting certain particles,  

In a decay reaction, the sum of the mass number and atomic number of the elements in the reactants and products must be the same

So the mass number of the element X = 238 - 4 = 234

Atomic number of the element X = 92 - 2 = 90

If we look at the periodic system, then the element with atomic number 90 is Thorium (Th)