Why is the method of using a density bottle more accurate than the measuring cylinder

While measuring relative density of liquids, two common method of measuring the volume are a measuring cylinder and a density bottle. Among these two method the density bottle gives more accurate measurement of the volume, resulting in more accurate determination of density or relative density

considering the question as per the attachment

here we can see that the radon nuclide has 222 as the atomic mass number and 86 as the atomic number.

when it undergoes nuclear fission it gives polonium which has atomic mass number as 218 and atomic number will be 84 along with a helium nucleus which has 4 atomic mass number and 2 as its atomic number.

222 = 218 + 4 (atomic mass number)

86 = ? + 2; therefore ? = 86-2 = 84.

the atomic mass number of polonium will be 84.

the correct answer would be b) volume versus temperature, because they are also directly proportional.