Select the correct answer
when phillip analyzed an unknown substance x, he found that it contained only one kind of atom. phillip was unable to convert the substance to
a simpler one. what is substance x?
oa. a compound
ob. an element
c. a heterogeneous mixture
od. a homogeneous mixture

B. an element

Explanation:

An atom is smallest indivisible particle that takes part in a chemical reaction. Different atoms due to the number of their protons called atomic number gives an element. Every element is a singular atom on it's own. Combination of atoms leads to the formation of molecules and compounds.

When compounds mix together without an actual chemical change, a mixture forms.

Elements are distinct substances that cannot be split up into simpler substances. They are usually made up of only one kind of atom.

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.