Final answer:
Lead-208 is likely the most abundant isotope of lead due to its high atomic mass and relative abundance, heavily influencing the average atomic mass of lead, which is 207.2.
Step-by-step explanation:
The average atomic mass of lead is 207.2, and this value is a weighted average of all the stable isotopes of lead present in nature, reflecting their relative abundances. Given the isotopes lead-204, lead-206, lead-207, and lead-208, and knowing that lead-208 has the highest atomic mass of 207.977, and the highest relative abundance at 52.40%, it is the isotope that most heavily influences the average atomic mass of lead. Therefore, the most abundant isotope of lead is likely to be lead-208 (d).