<span>the number of neutrons they have</span>
The bubbles indicate that there is a gas dissolved in the liquid, which may remain dissolved when the liquid is very cold, inside the refrigerator.
When the temperature of the liquid increases, it reduces its ability to dissolve the gas and the gas escapes (bubbles) from the liquid.
At the end, the behavior of the liquid permits you to conclude that the liquid is a mixture because it has a gas dissolved in it.
An electron has a relative mass of 0, whilst an alpha particle has a relative mass of 4
An electron has a relative mass of 0, whilst a proton has a relative mass of 1
A neutron has a relative mass of 1, whilst an alpha particle has a relative mass of 4
A neutron has a relative mass of 1, and a proton also has a relative mass of 1
