Subatomic particles in the Ca-48 2+ ion

Steps:

• Calcium's atomic number is 20, so neutral atom has 20 protons and 20 electrons.
• Mass number of 48 means neutrons = 48 - 20 = 28.
• The 2+ ion forms by losing 2 electrons, so electrons = 20 - 2 = 18.
• Protons and neutrons remain unchanged in the ion.

Why B is correct:

• Neutrons equal mass number minus atomic number (48 - 20 = 28); ionization does not affect neutrons.

Why the others are wrong:

• A: The ion has 18 electrons, not 20 (which is for the neutral atom).
• C: The ion has 18 electrons, not 22 (22 would imply a 2- ion).

Final answer: B