In radioactive alpha decay, the daughter nucleus has:

Correct answer: (d) Two protons and two neutrons fewer than its parent nucleus

Explanation

An alpha particle is a helium nucleus: 2 protons and 2 neutrons. When a nucleus gives out an alpha particle, the new (daughter) nucleus has:

• 2 protons fewer, so its atomic number falls by 2, and
• 2 neutrons fewer, so with the protons its mass number falls by 4.

For example, uranium-238 (atomic number 92) becomes thorium-234 (atomic number 90). In beta decay, by contrast, the atomic number rises by 1 and the mass number stays the same.