假如化學物A沸騰點比B低，用A溫度計可唔可以量度倒B沸騰點o既溫度?

The alcohol used in the thermometer is under pressure. As such, its boiling point has been raised so that it can be used to measure temperatures above its normal boiling point of 78'C.

Just look at the following web-page, in particular, pay attention to the temperarture range in the alcohol thermometer shown in the 'Picture of Thermometers', and its description under the [Description] section in D7.

http://www.phy.cuhk.edu.hk/contextual/heat/tep/act_thermometers_e.html

A代表酒精温度計
B代表水銀温度計
A可否量度到B在於温度,酒精温度計正常使用範圉0-100度C,水銀温度計可量度100度C以上,所以要先分折樣本沸點才有答案

You are mistaken. It is murcury that was used. Mercury is used for measuring high temperatures while alcohol is used for low temperatures.