The element with smallest size in the `4^(th)` peroid is

Options

A. calcium
B. potassium
C. rubidium
D. bromine

Answer

To determine the element with the smallest size in the 4th period of the periodic table, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Elements in the 4th Period:**
The 4th period of the periodic table includes the following elements:
- Potassium (K, Atomic number 19)
- Calcium (Ca, Atomic number 20)
- Scandium (Sc, Atomic number 21)
- Titanium (Ti, Atomic number 22)
- Vanadium (V, Atomic number 23)
- Chromium (Cr, Atomic number 24)
- Manganese (Mn, Atomic number 25)
- Iron (Fe, Atomic number 26)
- Cobalt (Co, Atomic number 27)
- Nickel (Ni, Atomic number 28)
- Copper (Cu, Atomic number 29)
- Zinc (Zn, Atomic number 30)
- Gallium (Ga, Atomic number 31)
- Germanium (Ge, Atomic number 32)
- Arsenic (As, Atomic number 33)
- Selenium (Se, Atomic number 34)
- Bromine (Br, Atomic number 35)
- Krypton (Kr, Atomic number 36)

2. **Understand Atomic Size Trends:**
As we move from left to right across a period in the periodic table, the atomic size generally decreases. This is because the number of protons in the nucleus increases, which increases the positive charge and pulls the electrons closer to the nucleus, resulting in a smaller atomic radius.

3. **Identify the Element with the Smallest Size:**
In the 4th period, the element that is furthest to the right is Bromine (Br). Since atomic size decreases across the period, Bromine will have the smallest atomic size among the elements in the 4th period.

4. **Conclusion:**
Therefore, the element with the smallest size in the 4th period is **Bromine (Br)**.

### Final Answer:
The element with the smallest size in the 4th period is **Bromine (Br)**.

---