South Korean stocks nosedived by more than 5 percent Monday, due largely to a risk-averse sentiment following the nomination of the new Federal Reserve chair, and a sharp decline in silver and gold prices. The Korean won plunged against the U.S. dollar. The benchmark Korea Composite Stock Price Index (KOSPI) tumbled 274.69 points, or 5.26 percent, to close at 4,949.67, snapping a four-session winning streak. The country's main bourse operator, the Korea Exchange (KRX), issued a sell-side