The atmospheric characterisation of exoplanets is a central objective in present-day astronomy, especially with the capabilities of JWST and other upcoming observatories like PLATO. The spectra of exoplanet atmospheres offer insights into their atmospheric composition and thermal structure. Molecules like CO, CO2, CH4, H2O, NH3, and HCN, which are the building blocks for more complex organic molecules and significant reservoirs of elemental C-N-O, have been detected in exoplanet atmospheres. Among various parameters influencing atmospheric composition, metallicity plays a significant role. The effect of atmospheric metallicity on thermochemical equilibrium abundances is reasonably well-constrained, though its effect on the disequilibrium composition needs to be better constrained. In this talk, I will discuss the crucial disequilibrium processes and how it drive the atmospheric composition. I will present the comprehensive study of the effect of atmospheric metallicity on the composition of H2O, CO2, CO, CH4, NH3, N2, and HCN over a large parameter space of temperature, pressure, and atmospheric metallicity. I will also introduce the quenching processes in planetary atmospheres and discuss how these processes influence atmospheric composition. Finally, I will explain how quenching processes can be incorporated into atmospheric retrieval modelling and how it can provide better constraints on the posterior distributions compared to canonical retrieval modelling.