Final answer:
For the isotope 44Ca, there are 20 protons and 24 neutrons. This corresponds to answer D. The mass number of an isotope equals the sum of its protons and neutrons, with the atomic number denoting the number of protons.
Step-by-step explanation:
The element with the symbol Ca stands for calcium, and the number 44 represents the mass number of the calcium isotope. The mass number (A) is the sum of the protons and neutrons in the nucleus of an atom. Calcium's atomic number, which is the number of protons in the nucleus and also the number of electrons in a neutral atom, is 20. To find the number of neutrons, you subtract the number of protons (atomic number) from the mass number.
In the case of 44Ca, we calculate the number of neutrons as follows:
number of neutrons = mass number - atomic number = 44 - 20 = 24.
Therefore, for 44Ca, there are 20 protons and 24 neutrons, which corresponds to answer D.