Both `PH_(3)` and `NH_(3)` are Lewis bases, but basic strength of `PH_(3)` is less than that of `NH_(3)`. Explain. 

Explanation

.N.atom of `NH_(3)` or .P. atom of `PH_(3)` has a lone pair of electrons available for donation. Hence `NH_(3) and PH_(3)` are Lewis bases. The electron pair density on a larger .P. atom is less than that on smaller .N.atom. Hence `PH_(3)` is a weaker base.