By natural radioactivity 238 U emits an -particle. The heavy residual nucleus is called UX 1 .

By natural radioactivity ²³⁸U emits an α-particle. The heavy residual nucleus is called UX₁. UX₁ in turn emits a beta particle. The resultant nucleus is called UX₂. Determine the atomic number and mass number for 

(a) UX₁ and 

(b) UX₂.