What is the frequency of a photon? During emission spectrum $$\Delta E=h\nu,$$
where $\nu$ is the frequency.
All books write that it is the frequency of photon, but photon is a particle and not a wave.
More than that what this frequency actually is?
Is it the frequency at which energy packets are released?
This wave and particle nature is causing conflict!
What is the meaning of frequency of photon?
I mean it is a particle and not a wave and frequency is a physical quantity associated with a wave.
 A: 
But photon is a particle and not a wave!!!

Not really, no. That is a simplified picture but it's not the full thing.
A better statement is that a photon is a discrete excitation of a given mode of the electromagnetic field. If that (classical) field mode is monochromatic, then the frequency of the photon will be the frequency of the mode.
Note that it is also possible to have single-photon states that do not have a well-defined frequency, which are formed by taking a quantum-mechanical superposition of states with well-defined frequencies over a range of such frequencies.
A: The frequency of light is a well defined concept, describing the electromagnetic spectrum . That light is a superposition of photons is also an experimental fact, as seen in this single photon double slit interference , where the interference pattern characteristic of the wave is built up one photon at a time.
In the quantum mechanical framework, the  photon,  as all  elementary particles, has a probability to materialize at an $(x,y)$ of the screen, given by the $Ψ^*Ψ$ of its wavefunction, so the frequency must reside  in the wavefunction of the photon, this is an example of the form :

Now write the complex wave function as a sum of real and imaginary parts $\overline E_T(\overline r)$ and $\overline B_T(\overline r)$,
$$
\overline{\psi}_T(\overline{r}, t) = 2^{-1/2}\left(\overline E_T(\overline r,t)+i \overline B_T(\overline r,t)\right)
$$

The published paper is here.
Superposition means the addition of the individual complex  wave functions before taking the overall $Ψ^*Ψ$, and as the E and B fields are the same as in the classical equation, the frequency of light is built up by the probability distributions of the superposed photons.
Thus the association of the classical frequency of light with the $ν$  in the definition of the energy of the photon $E=hν$ is outlined
In this link it is outlined  how the classical fields emerge from the quantum field theoretical framework.
