Correct Answer - Option 3 : I

ECO = I

_{CBO}/(1 - x)

**Expression of Collector current in CE configuration:**

In CE configuration, IB is input current and I_{C} is output current.

We know that,

I_{E} = I_{B} + I_{C} …. (1)

In CB cofiguration, The expression of collector current is written as,

I_{C} = xI_{E} + I_{CBO} …. (2)

From equation (1) and (2),

I_{C} = x (I_{B} + I_{C}) + I_{CBO}

I_{C} (1 – x) = αI_{B} + I_{CBO}

\(I_C=\frac{x}{1-x}I_B+\frac{1}{1-x}I_{CBO}\)…. (3)

From equation (3), it is apparent that if I_{B} = 0, the collector current will be equal to the collector to emitter cut-off current (ICEO).

This is abbreviated as I_{CEO}, meaning Collector-Emitter current with base open.

∴**IECO = ICBO/(1 - x)**