Given data:
Reverse saturation current, Is = 10^-10 A
Non ideality factor, n = 2
Diode voltage, Vd = 0.9V

To find:
Diode current, Id

Solution:
The current-voltage relationship of a diode is given by the Shockley equation:

Id = Is * (e^(Vd/(n*Vt)) - 1)

where Vt = kT/q is the thermal voltage, k is the Boltzmann constant (1.38 x 10^-23 J/K), T is the temperature in Kelvin, and q is the charge of an electron (1.6 x 10^-19 C).

Substituting the given values, we get:

Id = 10^-10 * (e^(0.9/(2*0.026)) - 1)
= 34.9 * 10^-3 A
= 35 mA

Therefore, the diode current is 35 mA (option B).

Explanation:
- The reverse saturation current Is is the current that flows through the diode when it is reverse biased (i.e., the voltage across it is negative). It is a small current that is due to minority carriers in the diode.
- The non ideality factor n is a parameter that takes into account the fact that real diodes don't behave exactly like ideal diodes. In particular, it models the fact that the current-voltage relationship of a diode is not perfectly exponential.
- The diode voltage Vd is the voltage across the diode when it is forward biased (i.e., the voltage across it is positive). It is the voltage at which the diode starts to conduct current.
- The Shockley equation is an empirical equation that models the current-voltage relationship of a diode, taking into account both the forward and reverse bias regions. It is based on the physics of pn junctions, which are the basic building blocks of diodes.
- The thermal voltage Vt is a parameter that depends on the temperature of the diode. It represents the voltage that is equivalent to the thermal energy per electron at that temperature.
- By substituting the given values into the Shockley equation and solving for Id, we get the diode current.