In a molecule (consider NH3) there are three sigma bond and lone pair hybridization is sp3. SP3 is formed because of combination of 1s orbital and 3p orbital ( i.e Px,Py and pz) or I can consider it a combination of 1s orbital Px and Py. Nitrogen has electronic combination in excited state as 2S1 2P4 where last electron goes in Pz orbital. So it is not actually the combination of three orbital . which amongst this explanations may I consider the true one for sp3 with lone pair and 3 bond pairl
And now total excited electrons are 4 which are shared in its excited state......with only bond pairs, so its h.s is sp3
In excited state its configuration is 2s1, 2p3.......not 2p4, as p orbital only accommodate 3 electrons, u have heard NH 4 + ion, it is always positively charged in any compound.