Alpha decay identification from mass and atomic number changes

Steps:

• Compare mass numbers: 226 (Ra) to 222 (Rn), decrease of 4.
• Compare atomic numbers: 88 (Ra) to 86 (Rn), decrease of 2.
• These changes match alpha particle emission (^{4}_{2}He), which reduces mass by 4 and atomic number by 2.
• No other particle fits both changes simultaneously.

Why B is correct:

• Alpha decay emits a helium nucleus (^{4}_{2}He), exactly accounting for the loss of 4 in mass number and 2 in atomic number per nuclear decay law.

Why the others are wrong:

• A: Beta decay would change atomic number by 1 without mass change, not observed here.
• C: Beta decay alters atomic number by ±1 but leaves mass number unchanged.
• D: Neutron emission reduces mass by 1 without affecting atomic number.

Final answer: B