MCQ Detailed View

Oxidation states help us understand electron distribution in compounds. In phosphorus oxoacids, phosphorus can exhibit multiple oxidation states depending on the number of oxygen atoms bonded to it.

Let’s calculate the oxidation state of phosphorus in the given compounds:

1. 
   

   H₃PO₄ (Phosphoric acid)
   Hydrogen = +1, Oxygen = -2
   3(+1) + P + 4(-2) = 0 → P = +5

   
   


2. 
   

   H₃PO₃ (Phosphorous acid)
   3(+1) + P + 3(-2) = 0 → P = +3

   
   


3. 
   

   H₃PO₂ (Hypophosphorous acid)
   3(+1) + P + 2(-2) = 0 → P = +1 

   
   


4. 
   

   H₂P₂O₇ (Pyrophosphoric acid)
   2(+1) + 2P + 7(-2) = 0 → P = +5

   
   

From the calculation, only H₃PO₂ has phosphorus in the +1 oxidation state. This is because hypophosphorous acid has fewer oxygen atoms than H₃PO₃ and H₃PO₄, which reduces the oxidation number of phosphorus.

Understanding oxidation states is crucial in inorganic chemistry, as it helps predict redox reactions, acidity, and chemical reactivity. Compounds like H₃PO₂ are used as reducing agents, partly due to the low oxidation state of phosphorus, making them effective in donating electrons during reactions.

In summary, H₃PO₂ is the compound where phosphorus exhibits the +1 oxidation state, distinguishing it from other phosphorus oxoacids. This concept is important for students studying redox chemistry and phosphorus compounds.