The mass number of a nucleus is A. Always less than its atomic number B. Always more than its atomic number C. Always equal to its atomic number D. Sometimes more and somtimes equal to its atomic number

The correct answer is: B. Always more than its atomic number.

The atomic number of an element is the number of protons in the nucleus of an atom of that element. The mass number of an element is the total number of protons and neutrons in the nucleus of an atom of that element. Therefore, the mass number of an element is always greater than or equal to its atomic number, because it always has at least one neutron.

Option A is incorrect because the mass number of an element is always greater than or equal to its atomic number.

Option B is correct because the mass number of an element is always greater than its atomic number.

Option C is incorrect because the mass number of an element is always greater than or equal to its atomic number, but it is not always equal to its atomic number.

Option D is incorrect because the mass

number of an element is always greater than or equal to its atomic number, but it is not always more than its atomic number.