To solve this question, the user needs to know the definition of thermal voltage and its value at room temperature.

Thermal voltage (VT) is the voltage equivalent of the thermal energy of a particle. It is given by the formula:

VT = kT/q

where k is the Boltzmann constant, T is the temperature in Kelvin, and q is the charge of a particle.

At room temperature (300K), the value of VT can be calculated as:

VT = (kT/q) = (1.38 x 10^-23 J/K x 300K) / 1.6 x 10^-19 C

Simplifying this expression, we get:

VT = 0.0259 V = 25.9 mV

Therefore, the answer is:

The Answer is: C. 26 mV