If z - axis is the internuclear axis, which of the following combinations are not allowed ?
(i) 2s and 2s (ii) 1s and `2p_(x) ` (iii) `2pP_(y) and 2p_(y)`
(iv) `2p_(x) and 2p_(z)` (v) `2p_(z) and 2p_(z)` (vi) `2s and 2p_(z)`
(vii) `2p_(x) and 2p_(y)`.

Explanation

To determine which combinations of orbitals are not allowed when the z-axis is the internuclear axis, we need to analyze each combination based on the principles of orbital overlap. Let's go through each option step by step.

### Step-by-Step Solution:

1. **Combination (i): 2s and 2s**
- **Analysis**: Both are s-orbitals. S-orbitals are spherical and can overlap along any axis, including the z-axis.
- **Conclusion**: Allowed.

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