Final answer:
The presence of a strong m+¹² peak with relative intensity close to that of the m+¹ peak indicates the presence of Carbon-13, as it has a natural occurrence that can explain the m+¹² peak's intensity.
Step-by-step explanation:
The question details a compound that exhibits an m+¹ peak with a relative intensity of 84% and an m+¹² peak with a relative intensity of 80%. This pattern suggests the presence of an isotope with a natural abundance close to the observed intensity of the m+¹² peak. Carbon-13 is the isotope that meets this criterion, as carbon-12 does not have a significant m+¹² peak. Carbon-12 (¹²C) has a mass number of 12 and an atomic number of 6, meaning it contains six protons and six neutrons. In contrast, Carbon-13 (¹³C) has a mass number of 13 and an atomic number of 6, which means it has one additional neutron compared to carbon-12. Therefore, the presence of an intense m+¹² peak is a distinct indicator of Carbon-13.