1.

The atomic weight of `Cu` is `63.546`. There are only two naturally occurring isotopes of copper `.^(63)Cu` and `.^(65)Cu`. The natural abundance of the`.^(63)Cu` isotope must be approximately.A. `10%`B. `30%`C. `50%`D. `72.7%`

Answer» Correct Answer - D
`.^(63)Cu" ".^(65)Cu`
`%` abundance `x" "100-x`
Avg mass `=(M_(1)x_(1)+M_(2)x_(2))/(x_(1)+x_(2))`
`63.546 = (63xx x + 65(100-x))/(100)`
`6354.6=63x+6500-65x`
`2x = 145.4 rArr x =70%` .


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