In the structure of HNO3 molecule, N-O bond (121 pm) is shorter that N-OH bond (140 pm). why?

Explanation

Electronic configuration of nitrogen aim phosphorus in ground state is :
`N(Z=7) : 1s^2 2s^2 2p_x^1 2_y^1 2p_z^1`
`P(Z=15) : 1s^2 2s^2 2p^6 3s^2 3p_x^1 3p_y^1 3p_z^1`
Thus, electronic excitation from 3s to 3d-subshell in phosphorus is possible due to the availability of vacant 3d-orbitals in the valence shell: This give rise to five half filled orbitals, which can hyridise to give five equivalent `sp^3` d-hybrid orbitals resulting in the formation of pentahalides like `PCl_5`. Such excitations are not possible in nitrogen because d-orbitals are not present in the volence shell of nitrogen.