Why are units used that are to express the densities of gases different from those used to express the densities of solids or liquids

If the units for gases were the same as the units for numbers would be too small to be convenient.

For example, the density of iron is 7.87 g/cm³.

Using the same units, the density of hydrogen is 0.000 0899 g/cm³.

It is much more convenient to express the density in numbers that are easier to visualize: 0.0899 g/L, and that is still a small number.

Any photo? or something

Answer : option a) 84explanation :

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.