# Relative abundance of the isotopes of iridium

There are two stable isotopes of iridium, $\ce{^191Ir}$ and $\ce{^193Ir}$. If you randomly pick an iridium atom from a large collection of iridium atoms, which isotope are you more likely to select?

• It depends on which isotope is more abundant. There should be tabulated values of these; a quick internet search will throw them up.
– user7232
Sep 17, 2014 at 11:57
• even in the exams right ? Sep 17, 2014 at 12:13
• Clearly not, but you'd expect such information to be given to you.
– user7232
Sep 17, 2014 at 12:38

An urn contains nothing but

• 63 white balls and
• 37 black balls.

You grab into the urn, pick one item, look at it and put it back.

What is the probability that you drew:

• a ball
• a white ball
• a black ball
• a red ball?
• 1) 100% 2)63% 3)37% 4)0% Sep 17, 2014 at 11:28
• @shaima Exactly :) Amazingly, 63% and 37% are roughly the abundancies of the two natural iridium isotopes: $\ce{^{193}Ir}$ and $\ce{^{191}Ir}$ Sep 17, 2014 at 11:33