The growth of urbanization and factories has resulted in significant issues related to the emission of harmful gases that are detrimental to the world at large. The contamination of air-causing gases can damage the health of humans and even result in death if long-term exposure is done. Several hazardous gases produced by industry and households like CO, NH3, H2S, and SO2 may affect the respiratory system and even result in cancer. Consequently, it is essential to develop highly selective and sensitive gas sensors for the purpose of monitoring these gases. Various gas-sensing methods and materials are studied and developed by various researchers. Among them, the most effective are used to solve environmental problems. The nanomaterials based on metal oxides are found to be very efficient gas sensors due to their several fascinating properties with high surface area, porosity, and absorption capacity that enhance their gas sensitivity.