Which property decreases from left to right across the periodic table and increases from top to bottom?

Options

A. (i) only
B. (i) , (ii) and (iii)
C. (i), (iii) and (iv)
D. (i) and (iv)

Explanation

To solve the question of which property decreases from left to right across the periodic table and increases from top to bottom, we will analyze the four properties mentioned: atomic radius, electronegativity, ionization energy, and melting point.

### Step-by-Step Solution:

1. **Understanding Atomic Radius:**
- **Left to Right:** As we move from left to right across a period, the atomic radius decreases. This occurs because the effective nuclear charge increases, pulling the electrons closer to the nucleus and resulting in a smaller atomic size.
- **Top to Bottom:** As we move down a group, the atomic radius increases. This is due to the addition of electron shells, which outweighs the increase in nuclear charge, leading to a larger atomic size.

**Conclusion:** Atomic radius decreases from left to right and increases from top to bottom.

2. **Understanding Electronegativity:**
- **Left to Right:** Electronegativity increases from left to right across a period. This is because the effective nuclear charge increases, allowing the nucleus to attract shared electrons more strongly.
- **Top to Bottom:** Electronegativity decreases from top to bottom in a group due to the increase in atomic size and the shielding effect, which reduces the nucleus's ability to attract electrons.

**Conclusion:** Electronegativity increases from left to right and decreases from top to bottom.

3. **Understanding Ionization Energy:**
- **Left to Right:** Ionization energy increases from left to right across a period. The increase in effective nuclear charge makes it harder to remove an electron.
- **Top to Bottom:** Ionization energy decreases from top to bottom in a group because the outer electrons are farther from the nucleus and are more easily removed.

**Conclusion:** Ionization energy increases from left to right and decreases from top to bottom.

4. **Understanding Melting Point:**
- **Left to Right:** The melting point does not follow a consistent trend across a period; it may increase and then decrease depending on the elements.
- **Top to Bottom:** Generally, the melting point decreases down a group due to the increase in atomic size and changes in bonding.

**Conclusion:** Melting point does not consistently decrease from left to right or increase from top to bottom.

### Final Answer:
The only property that decreases from left to right across the periodic table and increases from top to bottom is **atomic radius**.