Three quantum numbers are required to define an orbital while four quantum numbers are required to describe an electron.
Which of the following statements is correct for H atom? 

Options

A. H atom can be placed both in Group 1 and Group 18.
B. H atom can be placed both in Group 1 and Group 17.
C. H atom produces smallest anion in reality.
D. 2s 2p 3s orbitals are not available in H atom.

Answer

To determine which statements are correct for the hydrogen atom based on the provided information, we can analyze the quantum numbers and the properties of hydrogen.

### Step-by-Step Solution:

1. **Understanding Quantum Numbers**:
- Three quantum numbers (n, l, m_l) are needed to define an orbital:
- **n**: Principal quantum number (energy level)
- **l**: Azimuthal quantum number (subshell)
- **m_l**: Magnetic quantum number (orientation of the orbital)
- A fourth quantum number (m_s) is required to describe an electron:
- **m_s**: Spin quantum number (spin of the electron)

2. **Position of Hydrogen in the Periodic Table**:
- Hydrogen has one electron and can behave like an alkali metal (Group 1) by losing its electron to form H⁺.
- Alternatively, it can gain an electron to achieve a stable noble gas configuration, similar to halogens (Group 17), forming H⁻.

3. **Evaluating Statements**:
- **Statement 1**: Hydrogen can be placed in Group 1 or Group 17.
- This statement is **correct** because hydrogen can lose an electron (like alkali metals) or gain one (like halogens).

- **Statement 2**: Hydrogen atom produces the smallest radius.
- This statement is **false**. The hydrogen ion (H⁻) is larger than the hydrogen atom because it has an additional electron, resulting in a larger electron cloud.

- **Statement 3**: 2s and 2p orbitals are not available in hydrogen atom.
- This statement is **false**. While hydrogen only has one electron in the 1s orbital, the 2s and 2p orbitals are indeed available for higher energy states, but they are unoccupied in the ground state.

4. **Conclusion**:
- The correct statement regarding hydrogen is that it can be placed in Group 1 or Group 17.

### Final Answer:
The correct statement for the hydrogen atom is that it can be placed in Group 1 or Group 17.

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