Inorganic doubto

NH₃>NF₃>PH₃>PF₃

i think it must be ..........
NH₃>PH₃>NF₃>PF₃

NH₃ > NF₃ > PF₃ >PH₃

as PH₃ is highly unstable comp. as it has bond angle =91°

@ xyz drago's rule is applicable . so smalll -ve charge is on P in PH₃

@kartick jus now i checked with wiki.........
u r right.....[6].........
can u explain the drago's rule

this cn be analysed without using drago's rule also.

Comparing NF₃ and PF₃ , bond angle of NF₃ > PF₃ as N is more electronegative thn P ; thus N 's nucleus attracts bonded pairs more thn P. thus , the distance b/w bonded electrons is less in N, which increases its bond angle.

Here, P hs a lone pair but its effect is negligible. this is becoz, the lone pair is equitorial to 2 P - F bonds and 90⁰ repulsion to a P - F bond , but the bonded pair remains shifted towards F , thus ders minimum effect. but this effect is a bit more in NF₃ , as N is more e-ve thn P and bonded electrons remain less shifted towards F in it.

now comparing NF₃ and NH₃ , bond angle of NF₃ < NH₃ .

here, the lone pair effect is dominant. In NH₃ , 90⁰ repulsion b/w lone pair and axial N - H bond and here bonded e^-s remain shifted towards N. This effect is not available in NF₃.

same effect with PF₃ and PH₃

Now, among NF₃ and PH₃ , again the lone pair - bond pair repulsion comes into account, which would be dominant in PH₃ as the electrons remain shifted towards P.
thus , bond angle of NF₃ < PH₃ .

thus, finally bond angle order is : NH₃ > PH₃ > NF₃ > PF₃

might be. bt , i don't think, i hv analysed out smthing wrong, unless , ders some real exceptional case hidden in the question.