With reference to the variation of properties in the periodic table, which of the following is true?

Options

A. Atomic size increases from left to right across a period.
B. Ionisation potential increases from left to right across a period.
C. Electron affinity increases on going down a group.
D. Electronegativity increases on going down a group.

Explanation

To determine which of the statements regarding the variation of properties in the periodic table is true, we will analyze each statement step by step.

### Step 1: Analyze the first statement
**Statement:** Atomic size increases from left to right across a period.

- **Explanation:** As we move from left to right across a period, the number of protons in the nucleus increases, which leads to an increase in nuclear charge. This increased nuclear charge pulls the electrons closer to the nucleus, resulting in a decrease in atomic size. Therefore, this statement is **false**.

### Step 2: Analyze the second statement
**Statement:** Ionization potential increases from left to right across a period.

- **Explanation:** Ionization potential (or ionization energy) is the energy required to remove the outermost electron from an atom. As we move from left to right across a period, the atomic size decreases due to increased nuclear charge, making it more difficult to remove an electron. Thus, the ionization potential increases. Therefore, this statement is **true**.

### Step 3: Analyze the third statement
**Statement:** Electron affinity increases on going down a group.

- **Explanation:** Electron affinity is the energy released when an electron is added to an atom. As we move down a group, atomic size increases due to the addition of electron shells, which increases the distance between the nucleus and the outermost electrons. This results in a weaker attraction for the added electron, leading to a decrease in electron affinity. Therefore, this statement is **false**.

### Step 4: Analyze the fourth statement
**Statement:** Electronegativity increases on going down a group.

- **Explanation:** Electronegativity is the tendency of an atom to attract shared electrons in a bond. As we move down a group, atomic size increases, and the increased distance between the nucleus and the outermost electrons results in a weaker attraction for shared electrons. Thus, electronegativity decreases down a group. Therefore, this statement is **false**.

### Conclusion
After analyzing all the statements, the only true statement is that **ionization potential increases from left to right across a period**.

### Summary of True/False Statements:
1. Atomic size increases from left to right across a period - **False**
2. Ionization potential increases from left to right across a period - **True**
3. Electron affinity increases on going down a group - **False**
4. Electronegativity increases on going down a group - **False**