Final answer:
The naturally occurring isotope of strontium expected to have the highest natural abundance is Strontium-88 (Sr-88), as it is the closest to the average atomic mass of strontium listed as 87.62 atomic mass units (amu).
Step-by-step explanation:
Based on the average atomic mass of strontium listed on the periodic table as 87.62 atomic mass units (amu), we can infer which naturally occurring isotope of strontium has the highest natural abundance. Isotopes with atomic masses closer to the average atomic mass are generally more abundant. Among the options given, Strontium-88 (Sr-88) is closest to the average atomic mass of 87.62 amu. Therefore, Sr-88 would be expected to have the highest natural abundance. Moreover, natural abundance patterns suggest that the most stable isotopes with a number of neutrons and protons that is near a magic number (a concept from nuclear physics indicating a more stable configuration) are usually more abundant.