The correct answer is C. 1.0187 volts.
A Weston cell is a type of electrochemical cell that is used as a reference electrode. It has a stable voltage that is independent of temperature and time, making it ideal for use in calibrating other voltage sources. The Weston cell is named after its inventor, Edward Weston.
The Weston cell consists of a cathode made of mercury and a silver anode immersed in a saturated solution of cadmium sulfate. The cell reaction is as follows:
$$\ce{2Ag + Cd^2+ <=> 2Ag^+ + Cd}$$
The standard potential of the Weston cell is 1.0187 volts at 20°C. This means that if the cell is connected to a potentiometer, the voltage reading will be 1.0187 volts.
The other options are incorrect because they do not represent the standard potential of the Weston cell. Option A is too low, option B is too high, and option D is not a valid voltage.