A uranium nucleus ( 92 U 235 ) undergoes an alpha emission followed by 2 beta emissions.

Given,

• Atomic number of uranium (Z) = 92
• Mass number of uranium (A) = 235

On emission of one α-particle — the atomic number decreases by 2 and the mass number decreases by 4.

Atomic number = 92 - 2 = 90

Mass number = 235 - 4 = 231

On emission of two β-particles — the atomic number increases by 1 for each β-particle and the mass number remains unchanged.

So, for emission of two β-particles:

Atomic number = 90 + 2 = 92

Mass number = 231

Hence, the daughter nucleus has atomic number 92 and mass number 231.