[Nemesisof99]

When it is said that N₂O₃ is more acidic than P₂O₃, what actually shows the acidity of nitrogen trioxide? Is it that the two nitrogen atoms can accept an electron pair, thereby being a Lewis acid? Can you please tell me of a few instances where this happens?

[Schrödinger]

Think in terms of non-metallic nature.

Non-metallic oxides + water = acid

hope this helps

[Grundalizer]

Pretty much what Schrodinger said.

Do the reaction of both N2O3 and P2O3 with water, what acids do you get?

Here is N2O3 to help get you started.

http://en.wikipedia.org/wiki/Dinitrogen_trioxide

[Nemesisof99]

Thanks..still tryin to get my basics clear. I like inorganic chemistry now. 

[BluRay]

When it is said that N₂O₃ is more acidic than P₂O₃, what actually shows the acidity of nitrogen trioxide? Is it that the two nitrogen atoms can accept an electron pair, thereby being a Lewis acid?

Yes. 

Can you please tell me of a few instances where this happens?

BF₃ + NH₃ --> F₃B-NH₃
Boron accept a lone pair from nitrogen forming a covalent bond.
Others are, e.g., here:

http://en.wikipedia.org/wiki/Lewis_acids_and_bases

[aieeee]

one more thing :
P2O3 on hydrolysis provides one acid , while N2O3  provides us with two acids.

[Schrödinger]

one more thing :
P2O3 on hydrolysis provides one acid , while N2O3  provides us with two acids.

What does that have to do with acidity 

I mean, let's compare SO₃ and N₂O₃. When hydrolysed, the former produces H₂SO₄ and the latter gives 2 oxoacids of Nitrogen , both of which are weaker than H₂SO₄.

[AWK]

one more thing :
P2O3 on hydrolysis provides one acid , while N2O3  provides us with two acids.

Are you sure?

[Schrödinger]

one more thing :
P2O3 on hydrolysis provides one acid , while N2O3  provides us with two acids.

Are you sure?

@AWK: I am confused  . Which one is a mixed anhydride : N₂O₃ or N₂O₄?

Well, my guess   : N₂O₃ gives just HNO₂ on hydrolysis

[AWK]

http://en.wikipedia.org/wiki/N2O3

[BluRay]

@AWK: I am confused  . Which one is a mixed anhydride : N₂O₃ or N₂O₄?

The second:

N₂O₄ + H₂O    HNO₂ + HNO₃

[AWK]

What does mean term - mixed anhydride?

[Schrödinger]

I thought the term meant 'an anhydride that gives more than one acid on hydrolysis'.
i.e, It is 'made' of 2 acids.

[BluRay]

Exactly.
See for example pag 698, bottom left of this encyclopedia:

http://books.google.it/books?id=Owuv-c9L_IMC&printsec=frontcover&source=gbs_navlinks_s#v=onepage&q=&f=false