How many grams of naoh are needed to prepare 500 ml of 0.125 m naoh?

First let us calculate for the number of moles needed:

moles NaOH = 0.125 M * 0.500 L = 0.0625 mol

The molar mass of NaOH is 40 g/mol, hence the mass is:

mass NaOH = 0.0625 mol * 40 g/mol

mass NaOH = 2.5 grams

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.