b
The structures of all the oxo-acids of phosphorus are shown below :

The ratio is calculated as : \(\frac{\text { Reducing Hydrogen }}{\text { OH group }}\)

Orthophosphoric acid \(=\frac{0}{3}\)

Hypophosphorus acid \(=\frac{2}{1}\)

Phosphorus acid \(=\frac{1}{2}\)

Pyrophosphoric acid \(=\frac{0}{4}\)