`H_(3)overset(..)(O^(+))` has a lone pair of electrons bu due to the presence of +ve charge, it cannot donate its electron pair and hence it does act as a nucleophile. `R_(4)N^(+)`, however, does not have a lone pair of electrons, therefore, it does not act as a nucleophile.
`H_(3)overset(..)(O^(+))` has 8 electrons in the valence shell. It cannot expand its valence shell beyond 8 due to the absence of d-orbitals. Therefore, it does not act as an electrophile. Similarly, `R_(4)overset(+)(N)` also has 8 electrons in the valence shell. Like O, N also cannot expand its valence shell beyond 8 and hence it also does not act as an electrophile.
Thus, `H_(3)O^(+)` or `RN_(4)^(+)` neither acts as a nucleophile nor as an electrophile.
