Question

The formula of radium bromide is ${\mathrm{RaBr}}_2$. What is the formula of Radium phosphate?

Answer 1

It is given that the formula of Radium bromide is ${\mathrm{RaBr}}_2$

By applying the criss-cross method we can find the valency of Radium.

$$\begin{gathered} \mathrm{Symbols}\mathrm{Ra}\mathrm{Br} \\ \searrow \swarrow \\ \mathrm{Valency}21 \end{gathered}$$

Thus, the valency of Radium is found to be 2

Now, the molecular formula of Radium phosphate can be determined by the criss-cross method.

$$\begin{gathered} \mathrm{Symbol}\mathrm{Ra}{\mathrm{PO}}_4 \\ \searrow \swarrow \\ \mathrm{Valency}23 \end{gathered}$$

Hence, the molecular formula of Radium phosphate is ${\mathrm{Ra}}_3{\left({\mathrm{PO}}_4\right)}_2$