Which is better, mercury thermometers or alcohol thermometer

It depends on what you want to measure...
maybe i give you the adventages and disadventages of both thermometers.

Mercury thermometer:
it has high boiling points which will not boil when you measure something with really high temperature.But it has high melting point at the same time,so,when you measure something with low temperature,the mercury inside the thermometer may freeze and can't work.Also,mercury is a toxic substance,it's dangerous if you break the thermometer.

Alcohol thermometer:
it has low melting point which could measure the low temperature without freezing.And alcohol is a non-toxic substance,so it is safe for us to use even we break the thermometer.But it can't be used for measuring high temperature as alcohol has low boiling point,it will boil very easily.

therefore,it's better to use mercury one to measure high temperature but alcohol one to measure low temperature.If you want to be safe,alcohol one is better.