What is the use of thermometer?

The graph between two temperature scales $P$ and $Q$ is shown in the figure. Between upper fixed point and lower fixed point there are $150$ equal divisions of scale $P$ and $100$ divisions on scale $Q$. The relationship for conversion between the two scales is given by :

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Assertion: Water is considered unsuitable for use in thermometers.

Reason: This is due to small specific heat and high thermal conductivity.

Give one word for each of the following: 

All the temperatures, from lowest to highest, which a thermometer can measure

Represent the union of two sets by Venn diagram for each of the following.

$X=\{x | x$ is a prime number between $80$ and $100\}$

$Y=\{y | y$ is an odd number between $90$ and $100\}$

Assertion: Gas thermometers are more sensitive than liquid thermometers.

Reason: Coefficient of thermal expansion of gases is more than liquid.

The diagram shows two liquid-in-glass thermometers.

Which is more sensitive? Explain how you can tell.