|We analyze multi-wavelength emission observed during various phases of a B6.4 flare occurred on August 20, 2005 in order to explore the thermal and non-thermal emission mechanisms. Observations from several space and ground based observatories viz. RHESSI, TRACE, GONG and SoHO/EIT are employed in this study. Prolonged emission in soft X-ray waveband before the onset of the impulsive (pre-impulsive/precursor) phase is recorded. On the contrary, temporal evolution of X-ray emission does not show the presence of hard X-rays (>12 keV) emission in this phase. We synthesized X-ray images in 6-12 keV from RHESSI observations to study the X-ray source morphology. Next, we carry out in-depth analysis of chromospheric response in various phases of the flare employing high temporal cadence images of the Sun in Hα line centre as well as wings obtained from the Multi-channel Subtractive Double Pass Spectrograph (MSDP) at the Bialkow Observatory of the University of Wroclaw, Poland. Firstly we study various kinematic properties of different emission regions visible in the Hα images in the line centre as well as wings. In addition, the correlation study of the relative timing of X-ray and Hα emission profile in various phases of the flare is also made. Further, we use thermal plasma parameters estimated during the pre-impulsive and gradual phase to model the associated Hα emission. For the modeling we employ NLTE numerical codes modified for flare conditions. Next, we compare the synthesized and observed line profiles to explore plasma conditions during various phases of the flare.