Barium has 6 stable isotops (132Ba, 134Ba, 135Ba, 136Ba, 137Ba, and 138Ba) with natural abundances ranging from 0.1% for least abundant to 71.7% for the most abundant. Which isotope of barium is the most abundant? (Answer is 138Ba)
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about one minute with google will produce sources to that effect.
It was on a test and computer wasn't allowed.
Look up the atomic mass of Ba which from the periodic table is 137.32. That is the weighted average of all of the isotopes. Remember there is a mass defect when pushing protons and neutrons together in the nucleus which will cause the mass to be a little less than a whole number. So I would pick Ba138 as the most predominate. If 135 or 136 were more the average would be 135+ or 136+. At 137.3 we can guess that 138 is the most predominate and the presence of the lower mass numbers accounts for the decrease from 138.
To determine which isotope of barium is the most abundant, we need to compare the natural abundances of each isotope. The isotope with the highest natural abundance will be the most abundant.
Given that the natural abundances of the barium isotopes range from 0.1% to 71.7%, we can see that the isotope with the highest natural abundance is 138Ba, which has a natural abundance of 71.7%. Therefore, the most abundant isotope of barium is 138Ba.