Why on hot days the mercury inside a thermometer moves up and on cooler days it moves downs

When it is hot, the heat causes the mercury inside the thermometer to expand, and so that is why it moves UP.
However, when it's cold, the cold causes the mercury inside the thermometer to contract, and so that is why it moves DOWN.

       

Explanation:

Translation:

What volume will 12g of iron occupy?

Solution

Iron is a solid substance at room temperature. You can find the volume of solids (and of not solids) using the density.

     

You can obtaindthe density of most pure substances in the internet. The density of iron at room temperature is 7.874 g/cm³.

Thus, substituting in the formula, you get:

     

The answer is rounded to two significant figures because the input, 12g, has two significant figures.