92U238 → 82Pb206
Change in mass number = 238 - 206 = 32
The mass number changes only because of α-particle emission
Hence, number of α-particles emitted = 32/4 = 8
After emission of 8 α-particles, the atomic number should change by 2 x 8 = 16
Actual change in atomic number = 92 - 82 = 10
Hence, number of β-particles emitted = 16 - 10 = 6