Concept:Angles in the same segment of a circle are equal.Explanation:Since O is the centre, P,Q,R and S lie on the circumference of the circle.From the diagram, ∠RPQ=80∘ because ∠RPQ and ∠QSR are in the same segment, standing on chord RQ.The ray PR divides ∠QPS into ∠RPQ and ∠SPR.So, ∠QPS=∠RPQ+∠SPR.Thus, 100∘=80∘+∠SPR.This gives ∠SPR=100∘−80∘=20∘.Now, ∠SPR and ∠SQR are in the same segment because both stand on chord SR.Therefore, ∠SQR=∠SPR=20∘.Answer:A. 20∘