Question

Isotones are the atoms of different elements having:

• A. Same mass number
• B. Same atomic number
• C. Same number of neutrons
• D. Same number of electrons

Hint:

Isotones are characterized by having the same number of neutrons, which differentiates them from isotopes and isobars.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept.
Isotones are atoms of two different elements that are grouped together because of a shared property in their nucleus, and we need to identify which property that is.

Step 2: Key Idea.
For two atoms of different elements, the number of neutrons is found by subtracting the atomic number from the mass number. When this subtraction gives the same result for both atoms, they are isotones.

Step 3: Working through an example.
Take silicon-30 (atomic number 14, so neutrons = 30 minus 14 = 16) and phosphorus-31 (atomic number 15, so neutrons = 31 minus 15 = 16). Both have 16 neutrons even though their mass numbers, atomic numbers, and electron counts are all different.

Step 4: Final Answer.
Isotones share the same number of neutrons.

Answer 2

Every atom is built from three counts, protons, neutrons, and electrons, and each option in this question is really asking which of these three counts is being held fixed for isotones.

1. Same mass number: The mass number combines protons and neutrons together into one total, so fixing this total while letting the atomic number change describes isobars, a separate relationship from isotones.
2. Same atomic number: The atomic number is the count of protons, and it is what defines an element's identity. Two atoms of different elements can never share this count, so it cannot be the fixed property here.
3. Same number of neutrons: Boron-12 has 5 protons and 7 neutrons, while carbon-13 has 6 protons and 7 neutrons. Both carry 7 neutrons despite being different elements with different mass numbers, matching the isotone pattern exactly.
4. Same number of electrons: In a neutral atom the electron count always matches the proton count, so this reduces back to the atomic number, which different elements cannot share.

Sorting the options by which nuclear count is held fixed shows that only the neutron count, verified with the boron-12 and carbon-13 example, matches the isotone relationship.

Therefore, the correct answer is same number of neutrons.