Hydrogen is a pure substance represented by the chemical symbol H. Which of the following best describes hydrogen?
A. Hydrogen is a compound made of two or more kinds of atoms.
B. Hydrogen is an element made of only one kind of atom.
OC. Hydrogen is an element made of two or more kinds of atoms.
D. Hydrogen is a compound made of only one kind of atom.

B is the answer

Explanation:

Because it a molecular mass of one

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.