I'm very confused with search results I see on Google and different websites. I think the n-factor of H3PO4 is 3 because three H atoms are already bonded to three oxygen atoms. But some sources say it is 2, and I can't find out why.

  • $\begingroup$ If "these" sources say the $n$ factor is $2$, it may mean that they are speaking of an ion like $\ce{H2PO4^-}$. Can you mention the origin of these sources ? $\endgroup$
    – Maurice
    Dec 13, 2023 at 21:18
  • $\begingroup$ It can be 1, if being neutralized to H2PO4-, 2 if being neutralized to HPO4^2- or 3 if being neutralized to PO4^3-. $\endgroup$
    – Poutnik
    Dec 14, 2023 at 3:52
  • $\begingroup$ Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking. $\endgroup$
    – Community Bot
    Dec 14, 2023 at 23:43

1 Answer 1


The n-factor of a molecule is not absolute. It can change from reaction to reaction.

If we are talking about H3PO4 then it can have a wide variety of n factors. The oxidation state of phosphorus in this compound is +5.

So it can change to only lower oxidation states(+3, 0, -3) (redox) or not change at all(neutralization reaction.

In the first case(redox) the n factor depends upon the change in oxidation state. $$(+5\text{ to }+3):\text{ n factor is }2$$

In the second case that is in the neutralization reaction it depends on the basicity of phosphoric acid. $$\ce{ H3PO4\text{ to }H2PO4-}:\text{ n factor is }1.$$


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