Provided in question: Chord PQ is parallel to tangent at R.
To prove: R bisects the arc PRQ.
Proof:
Since PQ || tangent at R.
$\angle 1=\angle 2$ [alternate interior angles]
$\angle 1=\angle 3$ [angle between tangent and chord is equal to angle made by chord in alternate segment]
So, $\angle 2=\angle 3$
$\Rightarrow PR=QR$
Hence, clearly R bisects the arc PRQ.