Quark Transformation in β⁻ Decay

Steps:

• Neutron quark composition: one up quark and two down quarks (udd).
• Proton quark composition: two up quarks and one down quark (uud).
• In β⁻ decay, a neutron transforms into a proton, where one down quark converts to an up quark.
• Thus, the nucleus loses one down quark and gains one up quark overall.

Why A is correct:

• β⁻ decay involves a down quark decaying into an up quark via the weak interaction, decreasing the total number of down quarks by one in the nucleus.

Why the others are wrong:

• B: The number of down quarks changes due to the d → u transformation.
• C: While up quarks increase by one, the primary change emphasized is the decrease in down quarks from the decaying neutron.
• D: Up quarks increase as the down quark converts to an up quark.

Final answer: A