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 and the percentage abundance of 187Re as (100 - x).

We know that:

the average atomic mass of Re can be calculated using the formula:
ext{Average mass} = rac{(x imes 185) + ((100 - x) imes 187)}{100}

Setting this equal to the relative atomic mass of Re (186.2):
186.2 = rac{(x imes 185) + ((100 - x) imes 187)}{100}

Multiplying through by 100 yields:

$18620 = 185x + 18700 - 187x$

Combining like terms gives us:

$2x = 18700 - 18620$
$2x = 80$
$x = 40$

This means the percentage abundance of 185Re is 40%, thus the percentage abundance of 187Re is: $100 - 40 = 60$.

Therefore, the closest percentage abundance of 187Re is 60.