An element, X has the following isotopic composition:
200X : 90% 199X : 8.0% 202X : 2.0%
The weighted average atomic mass of the naturally occurring element X is closest to
(a) 201 amu
(b) 202 amu
(c) 199 amu
(d) 200 amu
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Answer - (d) 200 amu
Average atomic mass = sum of masses of its isotopes multiplied by the percentage/ratio of abundance in nature.
Atomic mass of X = $(200×90)+(199×8)+(202×2)\over100$
Atomic mass of X = 199.96 amu
Approximately = 200 amu