Which of the following steps is incorrect while constructing an angle of `120^(@)`?
Step I: Draw any line PQ and take a point O on it.
StepII: Place the pointer of the compass at O and draw an arc of convenient radius which cuts the line at A.
Step -III: Without disturbing the radius on the compass draw an arc with A as centre which cus the first arc at B.
Step IV: Again without disturbing the radius on the compass and with B as centre, draw an arc which cuts the first arc at A.
Step V: Join OC. Then `/_COA` is the required angle whose measure is`120^(@)`

Options

A. Only step-IV
B. Both Step -II and Step -III
C. Only Step -III
D. Both Step -III and Step-IV

Explanation

To construct an angle of \(120^\circ\), let's analyze the steps provided and identify the incorrect one.

### Step-by-Step Solution:

1. **Step I**: Draw any line \(PQ\) and take a point \(O\) on it.
- This step is correct. We need a base line to start our construction.

2. **Step II**: Place the pointer of the compass at \(O\) and draw an arc of convenient radius which cuts the line at \(A\).
- This step is also correct. Drawing an arc from point \(O\) helps us establish a reference point \(A\).

3. **Step III**: Without disturbing the radius on the compass, draw an arc with \(A\) as center which cuts the first arc at \(B\).
- This step is correct. By keeping the compass radius the same and drawing an arc from \(A\), we find point \(B\) where the arcs intersect.

4. **Step IV**: Again, without disturbing the radius on the compass and with \(B\) as center, draw an arc which cuts the first arc at \(A\).
- This step is incorrect. After finding point \(B\), we do not need to draw another arc from \(B\) that intersects at \(A\). This step does not contribute to constructing the \(120^\circ\) angle.

5. **Step V**: Join \(OC\). Then \(\angle COA\) is the required angle whose measure is \(120^\circ\).
- This step is correct. Joining points \(O\) and \(C\) forms the angle we are interested in.

### Conclusion:
The incorrect step in the construction of the \(120^\circ\) angle is **Step IV**.