Which order of relative size amongst the following is incorrect ?

Options

A. `LI lt Na lt K`
B. `C lt Si lt Al`
C. `Mg gt Al lt Na`
D. `F lt CI lt Br`

Answer

To determine which order of relative size among the given elements is incorrect, we need to analyze the periodic trends in atomic size. Here’s a step-by-step solution:

### Step 1: Identify the Elements
First, we need to identify the elements mentioned in the question. From the video transcript, we have:
1. Lithium (Li)
2. Sodium (Na)
3. Potassium (K)
4. Carbon (C)
5. Silicon (Si)
6. Aluminum (Al)
7. Magnesium (Mg)
8. Fluorine (F)
9. Chlorine (Cl)
10. Bromine (Br)

### Step 2: Locate the Elements on the Periodic Table
Next, we locate these elements on the periodic table:
- Lithium (Li) is in Group 1, Period 2.
- Sodium (Na) is in Group 1, Period 3.
- Potassium (K) is in Group 1, Period 4.
- Carbon (C) is in Group 14, Period 2.
- Silicon (Si) is in Group 14, Period 3.
- Aluminum (Al) is in Group 13, Period 3.
- Magnesium (Mg) is in Group 2, Period 3.
- Fluorine (F) is in Group 17, Period 2.
- Chlorine (Cl) is in Group 17, Period 3.
- Bromine (Br) is in Group 17, Period 4.

### Step 3: Analyze the Trends in Atomic Size
1. **Group Trend**: Atomic size increases as you move down a group due to the addition of electron shells.
- For Li, Na, K: K > Na > Li (Correct order)

2. **Period Trend**: Atomic size decreases as you move from left to right across a period due to increasing nuclear charge.
- For C, Si, Al: C > Si > Al (Correct order)
- For Mg, Al, Na: Na > Mg > Al (Incorrect order, since Al should be smaller than Na and Mg)

3. **Halogen Trend**: Atomic size increases down the group.
- For F, Cl, Br: Br > Cl > F (Correct order)

### Step 4: Identify the Incorrect Order
From the analysis:
- The order of sizes for **Mg, Al, and Na** is incorrect. The correct order should be Na > Mg > Al, but the provided order states Al < Na < Mg, which is incorrect.

### Conclusion
The incorrect order of relative size among the elements is:
**Aluminum (Al) < Sodium (Na) < Magnesium (Mg)**.