Explanation:

?? Microbial Fuel Cells (MFCs) have been described as “bioreactors that convert the energy in the chemical bonds of organic compounds into electrical energy through the catalytic activity of microorganisms under anaerobic conditions”.
?? Microbial Fuel Cell (MFC) is a type of bioelectric chemical fuel cell system that generates electric current by diverting electrons produced from the microbial oxidation of reduced compounds is called fuel or electron donor on the anode to high-energy oxidized compounds including oxygen it is also called as an oxidizing agent or electron acceptor on the cathode through an external electrical circuit. The working of microbial fuel cell technology is based on the principle of redox reactions. Hence, statement 1 is correct.
?? Microbial Fuel Cell generates Direct current (DC) in millivolts. It has applications in various fields such as power generation systems, bio-recovery, waste-water treatment, etc. MFCs are attractive for power generation applications that require only low power, where replacing batteries may be impractical such as wireless sensor networks. Hence, statement 2 is not correct.
?? MFCs convert energy more efficiently than standard internal combustion engines, which are limited by the Carnot efficiency. In theory, a microbial fuel cell is capable of energy efficiency far beyond 50%. Hence, statement 3 is correct.