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Pineapple crown (PC), a waste natural material (WNM), is investigated in this work for knowing its effectiveness to prevent mild steel (MS) in 0.5 M NaCl. The PC is extracted into water (AEPC), and 50-400 mg L-1 of AEPC is directly mixed in NaCl solutions as an inhibitor. The AEPC has been tested by UV-vis (UVS) and FTIR spectroscopy (IRS). The MS corrosion, with various amounts of AEPC, has been investigated by open circuit potential (OCP), Tafel polarization curves (TP), and electrochemical impedance spectroscopy (EIS). The results have confirmed that AEPC significantly protects MS in NaCl, and the best performance is obtained for 300 mg L-1 of AEPC (91%). The surface pictures, clicked by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM), shows that AEPC has effectively protected MS in NaCl. To get more insights, quantum chemical calculations like DFT and MD simulations are also explored. Based on the overall investigation, a mechanism for corrosion prevention has also been proposed. Mixed mode of Adsorption of AEPC on MS is suggested responsible for lowering in corrosion rate based on standard Gibbs free energy of adsorption (ΔG ads 0) calculated from adsorption coefficient (K ads).