Question

Isotopes of an element contain:

• A. Equal number of protons and electrons
• B. Same number of protons, different number of neutrons
• C. Same number of neutrons, different number of protons
• D. Equal number of nucleons

Hint:

Isotopes stay the same element, so think about which particle count must remain fixed and which one is free to change.

Answer 1

The Correct Option is B

Step 1: The atomic number of an element, which fixes its chemical identity, is the number of protons in the nucleus. Every atom of a given element must have the same number of protons.

Step 2: Isotopes are atoms of the same element that differ only in mass number, which is the total count of protons plus neutrons in the nucleus.

Step 3: Since the proton count cannot change without changing the element itself, isotopes must differ in the number of neutrons they carry, while the proton number stays fixed.

Step 4: For example, carbon-12 has 6 protons and 6 neutrons, while carbon-14 has the same 6 protons but 8 neutrons. Both are carbon because the proton count is unchanged, but they are different isotopes because the neutron count differs.

Step 5: So isotopes of an element have the same number of protons but a different number of neutrons, which is option B.