To solve the question regarding the trend of metallic nature in the periodic table with the increase in atomic number, we will analyze the behavior of metallic character both across a period and down a group.
### Step-by-Step Solution:
1. **Understanding Metallic Character**:
- Metallic character refers to the tendency of an element to lose electrons and form positive ions (cations). Metals are generally good conductors of heat and electricity, have high melting and boiling points, and are malleable and ductile.
2. **Analyzing Periodic Trends**:
- **Across a Period**: As we move from left to right across a period in the periodic table, the atomic number increases. For example, in Period 2, the elements are Lithium (Li), Beryllium (Be), Boron (B), Carbon (C), Nitrogen (N), Oxygen (O), Fluorine (F), and Neon (Ne).
- Lithium and Beryllium are metals, Boron is a metalloid, and Carbon, Nitrogen, Oxygen, Fluorine, and Neon are non-metals.
- This shows that as we move from Li to Ne, the metallic character decreases.
3. **Conclusion for Period Trend**:
- Therefore, with an increase in atomic number across a period, the metallic character **decreases**.
4. **Analyzing Group Trends**:
- **Down a Group**: Now, let’s consider Group 1 (the alkali metals), which includes Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), and Cesium (Cs).
- As we move down the group, the atomic number increases (Li = 3, Na = 11, K = 19, Rb = 37, Cs = 55).
- Each successive element down the group is more metallic in character. For example, Lithium is less metallic than Sodium, which is less metallic than Potassium, and so on.
- This trend is due to the increasing size of the atoms and decreasing ionization energy, which makes it easier for these elements to lose their outermost electron.
5. **Conclusion for Group Trend**:
- Thus, with an increase in atomic number down a group, the metallic character **increases**.
6. **Final Answer**:
- In summary, with an increase in atomic number, the metallic nature of elements **decreases in a period** and **increases in a group**. Therefore, the correct option is **A: Decreases in a period, increases in a group**.
