Which of the following is/are correct pair regarding size ?

Options

A. `Zn gt Cu`
B. `N gt O`
C. `Al gt Ca`
D. `B gt C`

Answer

To determine which pairs regarding size are correct, let's analyze each option step by step.

### Step 1: Analyze the first option - Zinc vs. Copper
- **Zinc (Zn)** has an atomic number of 30, while **Copper (Cu)** has an atomic number of 29.
- Both elements are in the 3d transition series.
- Generally, as we move from left to right across a period, atomic size decreases due to increased nuclear charge (Z effect).
- However, Zinc has a full d-subshell (d10), which leads to a greater shielding effect compared to the nuclear charge.
- Therefore, Zinc is larger than Copper.

**Conclusion for Step 1:** Zinc has a greater size than Copper. **(Correct)**

### Step 2: Analyze the second option - Nitrogen vs. Oxygen
- **Nitrogen (N)** has an atomic number of 7, while **Oxygen (O)** has an atomic number of 8.
- As we move from left to right in a period, atomic size decreases due to increased nuclear charge.
- Oxygen has a greater nuclear charge, which pulls the electrons closer to the nucleus, resulting in a smaller atomic size compared to Nitrogen.

**Conclusion for Step 2:** Nitrogen has a greater size than Oxygen. **(Correct)**

### Step 3: Analyze the third option - Aluminum vs. Calcium
- **Aluminum (Al)** has an atomic number of 13, while **Calcium (Ca)** has an atomic number of 20.
- Aluminum is in group 13, and Calcium is in group 2.
- As we move down a group, atomic size increases due to the addition of electron shells.
- Calcium, being lower in the periodic table, has a larger atomic size than Aluminum.

**Conclusion for Step 3:** Aluminum does not have a greater size than Calcium. **(Incorrect)**

### Step 4: Analyze the fourth option - Boron vs. Carbon
- **Boron (B)** has an atomic number of 5, while **Carbon (C)** has an atomic number of 6.
- Both elements are in group 13 and 14 respectively.
- As we move from left to right in a period, atomic size decreases.
- Therefore, Boron has a greater size than Carbon.

**Conclusion for Step 4:** Boron has a greater size than Carbon. **(Correct)**

### Final Summary:
- **First option:** Correct (Zinc > Copper)
- **Second option:** Correct (Nitrogen > Oxygen)
- **Third option:** Incorrect (Aluminum < Calcium)
- **Fourth option:** Correct (Boron > Carbon)

### Final Answer:
The correct pairs regarding size are the first, second, and fourth options.

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