Beta decay conserves mass number and increases atomic number by 1

Steps:

• Magnesium has atomic number Z=12; β⁻ decay converts a neutron to a proton, so daughter nucleus X has Z=13.
• Mass number A is conserved in β decay, so X has the same A as magnesium.
• The equation is likely ^{P}{12}Mg → ^{Q}{13}X + ^0_{-1}β (or similar), where P=A for Mg and Q=A for X.
• Thus, P=22 (Mg mass number) and Q=13 (X atomic number).

Why C is correct:

• Option C (22 13) satisfies A conservation (P=22 for both) and Z increase (13=12+1) per β decay rules.

Why the others are wrong:

• A (22 11): Z=11 decreases instead of increasing by 1.
• B (23 11): A changes to 23 (violates conservation) and Z=11 decreases.
• D (23 13): A changes to 23 (violates conservation).

Final answer: C