Tin plunged the most in more than seven years in London following a wave of selling from China’s onshore metals market, where sentiment has soured as investors focus on signs of economic weakness. The metal, which is mostly used in soldering, dropped 6.3% to settle at $17 700 a metric ton on the London Metal Exchange, the biggest drop since September 2011. The decline tracked a sharp slump in prices as the evening trading session got underway on the Shanghai Futures Exchange.