Intrinsic electron concentration is a fundamental property of a semiconductor material, which represents the number of electrons in the conduction band at thermal equilibrium. It is denoted by "ni" and depends on the temperature of the material.

The intrinsic electron concentration in silicon at a given temperature can be calculated using the expression:

ni = Nc * Nv * exp(-Eg / (2 * k * T))

Where:
- Nc is the effective density of states in the conduction band
- Nv is the effective density of states in the valence band
- Eg is the energy gap between the valence band and the conduction band
- k is the Boltzmann constant
- T is the temperature in Kelvin

Let's calculate the intrinsic electron concentration in silicon at T=300K using the given options:

a) 1.5 * 10^10 cm^-3
b) 1.5 * 10^-10 cm^-3
c) 2.5 * 10^19 cm^-3
d) 2.5 * 10^-19 cm^-3

Calculation:
Given T = 300K

We know that Nc = 2 * (2πm*k*T / h^2)^(3/2) and Nv = 2 * (2πm*k*T / h^2)^(3/2), where m is the effective mass of electrons and h is the Planck's constant.

The energy gap for silicon is Eg = 1.12 eV

Substituting these values into the equation, we get:

ni = (2 * (2πm*k*T / h^2)^(3/2)) * (2 * (2πm*k*T / h^2)^(3/2)) * exp(-1.12 / (2 * k * T))

Simplifying this expression, we find:

ni ≈ 1.5 * 10^10 cm^-3

Therefore, the correct answer is option 'A' (1.5 * 10^10 cm^-3).

Explanation:
- Intrinsic electron concentration is the number of electrons in the conduction band at thermal equilibrium.
- It is calculated using the expression ni = Nc * Nv * exp(-Eg / (2 * k * T)).
- The values of Nc, Nv, Eg, k, and T are substituted into the equation to calculate ni.
- The correct answer is option 'A' (1.5 * 10^10 cm^-3) as it matches the calculated value.