Question

A compound of potassium is assigned the formula $K_{2}C{r}_2{O}_7$.

Give the formula of each of the ions in this compound?

Answer 1

In a compound, potassium always exists as an ion K${}^{+}$.
Two K${}^{+}$ ions produce a total charge of +2.
The negative ion must carry a charge of -2, i.e. $C{r}_2{O}_7^{2-}$
dichromate (VI) ion, $C{r}_2{O}_7^{2-}$