Atoms of the same element possessing identical mass but differing in half`-` life period are called `………………………….` .

Answer

To solve the question, we need to identify the term that describes atoms of the same element that have the same mass but different half-life periods. Here’s a step-by-step solution:

### Step 1: Understand the Concept of Isotopes
- Atoms of the same element have the same number of protons but can have different numbers of neutrons. These variations are called isotopes. However, isotopes typically differ in mass.

### Step 2: Define Half-Life
- Half-life is the time required for half of the radioactive nuclei in a sample to decay. Different isotopes can have different half-lives.

### Step 3: Identify the Term for Atoms with Identical Mass and Different Half-Lives
- The question specifies that we are looking for atoms of the same element that possess identical mass but differ in their half-life periods. This situation is characteristic of nuclear isomers.

### Step 4: Define Nuclear Isomers
- Nuclear isomers are states of a nucleus that have the same mass number but exist in different energy states. They can have different half-lives due to the different energy configurations of the nucleons.

### Final Answer
- Atoms of the same element possessing identical mass but differing in half-life period are called **nuclear isomers**.

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