Chess Tactics From The 50th World Junior & 29th Junior Girls Chess Championships U-20 In India : What Should White Play ?

From round (6) and in the diagrammed position white blundered with : 28.a3 ??  allowing the killer 28... Rxb2 and black won by force as follows : 29.Rxb2 Qxa3 30.Nd3 Nc4 31.Qg3 Qxc3+ (0-1)

White had at his disposal a simple move that should have ended the game in his favor .
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