Tracking nuclear composition through successive decays

Steps:

• Nucleus P: 144 neutrons (N), 93 protons (Z).
• α-decay removes 2n and 2p, so Q has N=142, Z=91.
• β⁻-decay converts 1n to 1p, so R has N=141, Z=92.
• Graph points plot N vs. Z; locate R at (Z=92, N=141).

Why A is correct:

• Point A matches R's exact composition (Z=92, N=141) per decay rules.

Why the others are wrong:

• B: Matches Q (Z=91, N=142), before β⁻-decay.
• C: Incorrect Z=93 post-decays.
• D: Wrong N=144, unchanged from P.

Final answer: A