- The question asks to identify which of the listed NTPC plants is not gas-based. NTPC operates power plants based on various fuel sources, primarily coal and natural gas. - A) Auraiya: NTPC Auraiya is a combined cycle gas power plant located in Uttar Pradesh. It is gas-based. - B) Aonla: NTPC Aonla is a gas-based combined cycle power plant located in Uttar Pradesh. It is gas-based. - C) Dadri: NTPC Dadri is a major power generation complex in Uttar Pradesh that includes both a coal- based thermal power plant (NTPC Dadri Thermal) and a gas-based power plant (NTPC Dadri Gas). Since it includes a gas-based component, it's not exclusively not gas-based, making it different from a purely non-gas plant. - D) Tanda: NTPC Tanda is a super thermal power plant located in Uttar Pradesh. It is a coal-based power plant. Its units use coal as fuel. - Therefore, Tanda is the plant that is not gas-based among the options.