下列物质的溶液能使酚酞试液变红色的是（　　）

$\frac{7.2}{x}=\frac{36}{0.5}$ ，则x=____

（用小数表示）

（18分）用沉淀滴定法快速测定NaI等碘化物溶液中c（I^﹣），实验过程包括准备标准溶液和滴定待测溶液．

Ⅰ准备标准溶液

a．准确称取AgNO₃基准物4.2468g（0.0250mol）后，配制成250mL标准溶液，放在棕色试剂瓶中避光保存，备用．

b．配制并标定100mL 0.1000mol•L^﹣1 NH₄SCN标准溶液，备用．

Ⅱ滴定的主要步骤

a．取待测NaI溶液25.00mL于锥形瓶中．

b．加入25.00mL 0.1000mol•L^﹣1 AgNO₃溶液（过量），使I^﹣完全转化为AgI沉淀．

c．加入NH₄Fe（SO₄）₂溶液作指示剂．

d．用0.1000mol•L^﹣1NH₄SCN溶液滴定过量的Ag⁺，使其恰好完全转化为AgSCN沉淀后，体系出现淡红色，停止滴定．

e．重复上述操作两次．三次测定数据如下表：

f．数据处理．

回答下列问题：

阅读短文，从方框中选择适当的动词，并用其适当形式填空。有的需要加助动词或不定式符号。（每词限用一次）

    Last weekend, Jim went to see a film. It was about a boy ____ Bob. Bob lived with his parents in a small town. They were very poor. Bob's father ____  in a market for a long time. Bob wanted ____ a bike very much.
    One day, an old man ____ down by some boys, and they ran away. Bob went to help the old man. The old man gave him a magic book and told Bob to make a wish before opening it.
    Can you guess what ____  in the end? Please watch the film and find out!

 某学习小组用KClO₃和MnO₂的混合物加热制取O₂，收集到4.8gO₂后停止加热，称得剩余固体的质量为28.0g，继续加热至不再产生O₂，最终剩余固体质量为23.2g，试计算（不考虑O₂的损耗）；