when structure of any compound is given then for predicting hybridisation we simply calculate number of sigma bond and say hybridisation (eg.3=sp2 5=sp3d 6-sp3d2 ) cant it be that s and d are getting hybridised and p remains unhybridised ? Also since s can not form pi bond whatever 1 bond formed has to be sigma and from s so is it that paired electron of s orbital must get unpaired even for molecules like O2 and its sp ???
Yes, it is possible that s and d gets hybidised. Such type of hybridisation is shown by Mn in MnO4- ion. Mn in MnO4- shows sd3 hybridisation.
Yes, paired electrons in s-orbital needs to be unpaired for forming a covalent bond.