12. Construct a right angle

Step 1: Draw a line segment $PA$.

 

Step 2: Place the protractor on the line segment $PA$ and the mid point of the protractor at point $P$, as shown in the figure.

 

 

Step 3: On $PA$ from the right side of the protractor start counting from $0°$ in the ascending order (counter-clockwise direction) and finally mark a point $Q$ using a sharp pencil at the point $90°$ on the semicircular edge of the protractor.

 

 

Step 4: Remove the protractor and join $PQ$.

 

We get the required angle $∠APQ$ $=$ $90°$.