Which of the following is/are correct for the formation of `pi` bond ?

Options

A. a. overlapping of `p_(x)-p_(x)`(`Z` internuclear axis)
B. b. overlapping of `p_(z)-p_(z)` orbitals(`Z` internuclear axis)
C. c. overlapping of `p_(y)-p_(y)` orbitals(`Z` internuclear axis)
D. d. overlapping of `s-p_(z)` orbitals (`Z` internuclear axis)

Explanation

To determine which options are correct for the formation of a pi bond, we need to analyze the overlapping of different types of orbitals as described in the question. Let's go through each option step by step.

### Step 1: Understanding Orbital Overlap
- **Pi Bond Formation**: A pi bond is formed by the sidewise (lateral) overlap of p orbitals. In contrast, a sigma bond is formed by head-on (end-to-end) overlap of orbitals.

### Step 2: Analyzing Each Option

#### Option A: Overlapping of px with px
- **Description**: The overlap occurs along the z-axis.
- **Analysis**: Since the px orbitals have two lobes that can overlap sidewise, this results in a pi bond formation.
- **Conclusion**: **Correct** (Pi bond is formed).

#### Option B: Overlapping of pz with pz
- **Description**: The overlap occurs along the z-axis.
- **Analysis**: The pz orbitals overlap head-on, which leads to the formation of a sigma bond, not a pi bond.
- **Conclusion**: **Incorrect** (Sigma bond is formed).

#### Option C: Overlapping of py with py
- **Description**: The overlap occurs along the z-axis.
- **Analysis**: Similar to option A, the py orbitals can also overlap sidewise, leading to the formation of a pi bond.
- **Conclusion**: **Correct** (Pi bond is formed).

#### Option D: Overlapping of s with pz
- **Description**: The overlap occurs between an s orbital and a pz orbital.
- **Analysis**: The s orbital overlaps head-on with the pz orbital, resulting in the formation of a sigma bond.
- **Conclusion**: **Incorrect** (Sigma bond is formed).

### Final Conclusion
The correct options for the formation of a pi bond are **Option A and Option C**.

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