The hypothesis states that the fraction of
radioactive nuclei after n half-lives is 0.51
In this expression, the value 0.5 represents
the fraction of nuclei still radioactive after any
half-life cycle.
the fraction of nuclei still radioactive at the
start of the experiment.
the amount of time it takes half of the
radioactive atoms to decay.
the number of half-life cycles.
DONE

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.

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged

It is a product

The population of unionid mussels decreased after zebra mussels were introduced. zebra mussels competed with the unionid mussels for food. the zebra mussels were able to displace the unionid mussels, allowing the zebra mussel population to increase  over the years. the unionid mussel population decreased because  of lack of food.