Which of the following represent increasing order of size of `4th` period element ?

Options

A. `K, Kr, Ca, Br`
B. `Kr, Br, Ca, K`
C. `K, Ca, Br, Kr`
D. `Br, Kr, Ca,K`

Answer

To determine the increasing order of size of the 4th period elements (Potassium, Calcium, Bromine, and Krypton), we need to analyze the atomic sizes based on their positions in the periodic table. Here's a step-by-step breakdown of the solution:

### Step 1: Identify the Elements and Their Groups
- **Potassium (K)**: Group 1 (Alkali metal)
- **Calcium (Ca)**: Group 2 (Alkaline earth metal)
- **Bromine (Br)**: Group 17 (Halogen)
- **Krypton (Kr)**: Group 18 (Noble gas)

### Step 2: Understand the Trend in Atomic Size
- Atomic size generally **decreases** from left to right across a period due to the increase in nuclear charge, which pulls the electrons closer to the nucleus.
- As we move from potassium to krypton, the atomic number increases, leading to a greater positive charge in the nucleus.

### Step 3: Compare the Sizes
- **Potassium (K)** has the largest atomic size because it is the furthest left in the period.
- **Calcium (Ca)** is smaller than potassium but larger than bromine and krypton.
- **Bromine (Br)** is smaller than both potassium and calcium due to its higher nuclear charge.
- **Krypton (Kr)**, being a noble gas, has a larger van der Waals radius compared to the covalent radii of bromine, making it larger than bromine.

### Step 4: Establish the Order of Size
Based on the above analysis, we can establish the order of size from largest to smallest:
1. Potassium (K) > Calcium (Ca) > Krypton (Kr) > Bromine (Br)

### Step 5: Write the Increasing Order
Since the question asks for the increasing order of size, we will reverse the order:
- **Increasing order of size**: Bromine (Br) < Krypton (Kr) < Calcium (Ca) < Potassium (K)

### Final Answer
Thus, the increasing order of size of the 4th period elements is:
**Bromine < Krypton < Calcium < Potassium**