阅读理解

Everybody wants to be healthy. You know food is very important. There are lots of healthy food. You can have more bananas, apples, oranges, tomatoes and lettuce because fruit and vegetables are good for you. But don’t eat too much chocolate. It’s not healthy food. Healthy food can make you grow (生长) and make you strong（强壮的） and happy. Remember there is a saying—“An apple a day keeps the doctor away（远离）”. Sports can also keep you healthy. Get up early and do some sports every day. Don’t be lazy（懒惰的）. You will be healthy and happy.

某研究性学习小组对Mg和Al的性质进行了下列的实验及研究．

（1）以镁条、铝片为电极，稀NaOH溶液为电解质构成的原电池（如图1所示）时发现，刚开始时，电流表指针向右偏转，镁条做负极；但随后很快指针又向左偏转，镁条表面有极少量的气泡产生．

①开始阶段，负极发生的反应是____ ．

②随后阶段，铝片发生的电极反应式是____ ；则镁电极发生的电极反应式是____ ．

（2）经研究测定，镁与不同浓度的硝酸反应，生成气体产物的含量随HNO₃浓度变化曲线如图2所示，溶液中的产物有Mg（NO₃）₂、NH₄NO₃和H₂O．96mgMg在1L4mol•L^﹣1的HNO₃中完全溶解，并可收集到22.4mL（标准状况下）气体（忽略反应过程中HNO₃浓度的变化），该反应的化学方程式是____ ．

在棱长为3厘米的正方体木块的正面的中心上打一个直穿木块的洞，洞口呈边长为1厘米的正方形，挖洞后木块的表面积是多少？