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Which are the isotone, isobar and isotope nuclei respectively of ¹²₆C from among ¹⁴₆C, ¹²₅B, ¹³₇N ?

Asked in GSEB Board March 2019 · Composition, isotopes and isobars

Answer: (3) ¹³₇N, ¹²₅B, ¹⁴₆C

Step-by-step solution

Given: ¹²₆C has Z=6, A=12 and so N=12-6=6.

Idea: isotones share N, isobars share A, isotopes share Z. Work out all three numbers for each candidate.

¹⁴₆C: Z=6, A=14, N=8 — the Z matches, so it is the isotope.

¹²₅B: Z=5, A=12, N=7 — the A matches, so it is the isobar.

¹³₇N: Z=7, A=13, N=6 — the N matches, so it is the isotone.

In the order asked — isotone, isobar, isotope — that is ¹³₇N, ¹²₅B, ¹⁴₆C.

Why the other options are wrong

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