A：铁和稀盐酸反应：2Fe+ 6H+=2Fe3++3H2↑
B：实验室用浓盐酸与MnO2反应制Cl2：MnO2+2H++2Cl- Cl2↑+Mn2++H2O
C：石灰乳与碳酸钠溶液混合：Ca2++CO2-3=CaCO3↓
D：硫酸氢钠溶液中加入氢氧化钡溶液至中性：2H++SO24++Ba2+2OH===BaSO4+2H2O
—Look! All students in the classroom are preparing for the coming exams_____.
—Yes, the exams are very important to them.
