The yen is set to slump to 125 against the dollar in 2017, with little chance of a sustained gain past 115, as the Federal Reserve’s policy tightening widens the interest-rate differential between U.S. and Japan, said Mansoor Mohi-uddin, a strategist at NatWest Markets, a unit of Royal Bank of Scotland Group Plc. The forecast shows Mohi-uddin, who previously estimated a trading range of 110 to 120 for the yen versus the greenback, has turned more bearish.