The answer is B. 25°C.
A temperature of 25°C can be considered as a room temperature. It is an optimal temperature for the most living beings which cell potential is considered as standard. It is known that at 100°C water boils, so this temperature cannot be standard, cells will degrade at this temperature. Similarly 0°C and –273°C are too cold, water of the cells will freeze, cells will freeze, and cell potential will not be optimal.
