It's simple, just follow my steps.
1º - in 1 L we have
of 
2º - let's find the number of moles.
3º - The concentration will be
But we have this reaction
This concentration will be the concentration of
![K_{sp}=\frac{[Ba^{2+}][CO_3^{2-}]}{[BaCO_3]}](https://tex.z-dn.net/?f=K_%7Bsp%7D%3D%5Cfrac%7B%5BBa%5E%7B2%2B%7D%5D%5BCO_3%5E%7B2-%7D%5D%7D%7B%5BBaCO_3%5D%7D)
considering![[BaCO_3]=1~mol/L](https://tex.z-dn.net/?f=%5BBaCO_3%5D%3D1~mol%2FL)
![K_{sp}=[Ba^{2+}][CO_3^{2-}]](https://tex.z-dn.net/?f=K_%7Bsp%7D%3D%5BBa%5E%7B2%2B%7D%5D%5BCO_3%5E%7B2-%7D%5D)
and
![[Ba^{2+}]=[CO_3^{2-}]=5.07\times10^{-5}~mol/L](https://tex.z-dn.net/?f=%5BBa%5E%7B2%2B%7D%5D%3D%5BCO_3%5E%7B2-%7D%5D%3D5.07%5Ctimes10%5E%7B-5%7D~mol%2FL)
We can replace it
Therefore the
is:
1º - in 1 L we have
2º - let's find the number of moles.
3º - The concentration will be
But we have this reaction
This concentration will be the concentration of
considering
and
We can replace it
Therefore the