In which of the following pairs, the first atom or ion is not larger than the second ?

Options

A. `K, K^(+)`
B. `S, O`
C. `Br, Br ^(-)`
D. `N,O`

Answer

To solve the question of which pair has the first atom or ion that is not larger than the second, we need to analyze the sizes of the atoms and ions involved in each pair. Let's break it down step by step:

### Step 1: Understand the Size of Ions
- **Cations** (positively charged ions) are smaller than their neutral atoms because they lose electrons, leading to a decrease in electron-electron repulsion and a stronger attraction between the remaining electrons and the nucleus.
- **Anions** (negatively charged ions) are larger than their neutral atoms because they gain electrons, leading to increased electron-electron repulsion.

### Step 2: Analyze Each Pair
1. **K and K⁺**:
- K (Potassium) is larger than K⁺ (Potassium ion) because K⁺ has lost an electron.

2. **S and O**:
- S (Sulfur) is larger than O (Oxygen) because as you move down a group in the periodic table, the size of the atoms increases due to the addition of electron shells.

3. **Br and Br⁻**:
- Br (Bromine) is smaller than Br⁻ (Bromide ion) because Br⁻ has gained an electron, making it larger than the neutral Bromine atom.

4. **N and O**:
- N (Nitrogen) is smaller than O (Oxygen) because they are in the same period, and as you move from left to right in a period, the size decreases due to increased nuclear charge.

### Step 3: Identify the Correct Pair
From the analysis:
- K > K⁺ (K is larger)
- S > O (S is larger)
- Br < Br⁻ (Br is smaller)
- N < O (N is smaller)

The pairs where the first atom or ion is not larger than the second are:
- **Br and Br⁻** (Br is smaller than Br⁻)
- **N and O** (N is smaller than O)

### Conclusion
The pairs in which the first atom or ion is not larger than the second are **Br and Br⁻** and **N and O**.