下列离子方程式正确的是 （ ）
A．碳酸氢钠溶液与少量石灰水反应 HCO3-+Ca2++OH-===CaCO3↓+H2O
B．氯化铵与氢氧化钠两种溶液混合加热 OH-+NH4+
H2O+NH3↑
C．氢氧化镁与稀硫酸反应 H++OH-===H2O
D．单质铜与稀硝酸反应 Cu+2H++2NO3-===Cu2++2NO↑+H2O
答案：B
本题考查的是离子方程式的书写判断。由于碳酸氢钠溶液与少量石灰水反应，其中碳酸氢钠溶液
过量，应书写为Ca2++2OH-+2HCO3-=CaCO3↓+2H2O+CO32-，故A错；C中氢氧化镁为弱电解质，不能拆分，
故C错；D项中元素未守衡，故D错。
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