Problem

Consider the following oxyanions :

\text{PO}_4^{3-}

\text{P}_2\text{O}_6^{4-}

\text{SO}_4^{2-}

\text{MnO}_4^-

\text{CrO}_4^{2-}

\text{S}_2\text{O}_5^{2-}

\text{S}_2\text{O}_7^{2-}

and find the value of

R + Q - P

Where

P

= Number of oxy anions having three equivalent X—O bonds per central atom

Q

= Number of oxy anions having two equivalent X—O bonds per central atom

R

= Number of oxy anions having four equivalent X—O bonds per central atom