Some information about the element rhenium (Re) is given in the table below - VCE - SSCE Chemistry - Question 3 - 2007 - Paper 1

Let the percentage abundance of 185Re be represented as x. Therefore, the percentage abundance of 187Re will be (100 - x).

Using the average atomic mass, we can set up the equation:

$186.2 = \frac{x \times 185.0 + (100 - x) \times 187.0}{100}$

Multiplying throughout by 100 to eliminate the fraction:

$18620 = x \times 185.0 + (100 - x) \times 187.0$

Expanding the right-hand side gives:

$18620 = 185x + 18700 - 187x$

Combining like terms results in:

$18620 - 18700 = -2x$

Thus,

\Rightarrow x = 40$$ Since x = 40, the percentage abundance of 187Re is: $$100 - x = 100 - 40 = 60$$ Therefore, the percentage abundance of 187Re is closest to 60.