Answer:
B. 138
Explanation:
Based on isotope notation:
[tex]^X_nA[/tex]
For the atom A, the mass number, X, is the sum of neutrons and protons and
n is the number of protons = Atomic number.
The number of protons depends of the nature of the atom. For example, Carbon has 12 protons, hydrogen 1 and Radium has 88 protons.
The radium-226 means the mass number is 226. Thus, number of neutrons are:
Mass number - Atomic number
226 - 88 = 138
Right answer is:
B. 138
