Which of the following pairs of atoms have same number of electrons in the outermost orbit

Options

A. `N-O`
B. `Na-Cl`
C. `Ca-Cl`
D. `Cl-Br`

Answer

To determine which pairs of atoms have the same number of electrons in their outermost orbit, we can follow these steps:

### Step 1: Identify the Groups of Elements
- First, we need to identify the groups of the elements in the given pairs. Elements in the same group of the periodic table have similar properties, including the number of electrons in their outermost shell.

### Step 2: Analyze the Given Pairs
- Let's analyze the pairs of atoms provided in the question. For example, if we have pairs like Sodium (Na) and Chlorine (Cl), Calcium (Ca) and Chlorine (Cl), and Chlorine (Cl) and Bromine (Br), we need to check their respective groups.

### Step 3: Determine the Number of Electrons in the Outermost Shell
- For each element, we can determine the number of electrons in the outermost shell:
- Sodium (Na) is in Group 1 → 1 electron in the outermost shell.
- Chlorine (Cl) is in Group 17 → 7 electrons in the outermost shell.
- Calcium (Ca) is in Group 2 → 2 electrons in the outermost shell.
- Bromine (Br) is in Group 17 → 7 electrons in the outermost shell.

### Step 4: Compare the Outermost Electrons
- Now, we compare the number of outermost electrons:
- Na (1) and Cl (7) → Different
- Ca (2) and Cl (7) → Different
- Cl (7) and Br (7) → Same

### Step 5: Conclusion
- From our analysis, the pair that has the same number of electrons in the outermost orbit is Chlorine (Cl) and Bromine (Br), both having 7 electrons in their outermost shell. Thus, the answer is option D.

### Final Answer:
The pair of atoms that have the same number of electrons in the outermost orbit is **Chlorine (Cl) and Bromine (Br)**.

---