Neutral particle pair with balanced charge and comparable mass

Steps:

• Identify charges: electron (-1), proton (+1), neutron (0).
• Calculate sum of charges for each option to find zero: only A sums to zero (-1 + 1 = 0); B sums to -1, C to +1, D to +1.
• Recall masses in u: electron ≈ 0, proton ≈ 1, neutron ≈ 1; carbon-12 atom = 12 u, so ½ mass = 6 u.
• Note no option sums to ~6 u (A/B ≈ 1 u, C ≈ 2 u, D ≈ 3 u), making mass condition unmet—question ambiguous.

Why B is not correct:

• Sum of charges is -1, not zero; violates charge neutrality.

Why the others are wrong:

• A: Charge sums to zero but mass ≈1 u ≠6 u.
• C: Charge sums to +1 ≠0.
• D: Charge sums to +1 ≠0; listed as three particles, not a pair.

Not enough information to match both conditions precisely.

Final answer: No valid option