What volume of ammonia, in dm, can be made from 30 dm of nitrogen and 60 dm of hydrogen?
Assume that all volumes are measured at the same temperature and pressure and that
the reaction goes to completion according to the equation:

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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.