For the silicon diode (assuming r_f to be zero), the value of I_D in figure is:

Concept:

At forward bias condition → Diode should be replaced with a battery source of value equal to its barrier potential(for silicon 0.7 V)circuit and the equivalent forward resistance r_f.

At reverse bias condition → Diode should be replaced with an open circuit.

Calculation:

In the given circuit arrangement the diode is in forward bias;

Then;

I_D = (8-0.7)/2.2 = 3.32 mA