Question

Question #a31cd

Answer 1

Those are mass numbers of each molecular isotope, meaning those of `"Br"_2`. Bromine is naturally a diatomic liquid.

It doesn't mean that there are three naturally-existing atomic isotopes, but it does mean that one `"Br"` on `"Br"_2` doesn't necessarily have to be `""_(35)^(81) "Br"` if the other is `""_(35)^(81) "Br"`, for example.

Add up the mass numbers and you should see that:

`79 + 79 = color(green)(158)`
`79 + 81 = color(green)(160)`
`81 + 81 = color(green)(162)`

That means you have the three naturally-existing isotopic molecules:

`color(blue)(""_(35)^(79) "Br"-""_(35)^(79) "Br")`

`color(blue)(""_(35)^(79) "Br"-""_(35)^(81) "Br")`

`color(blue)(""_(35)^(81) "Br"-""_(35)^(81) "Br")`

Therefore, you still have:

• Two naturally-existing atomic isotopes.
• Due to the diatomic nature of naturally-existing bromine liquid, three combinations of atoms are possible, generating three naturally-existing molecules containing the three different combinations of atomic isotopes.