Considering `X` axis as the inter nuclear axis, which out of the following will form a sigma bond
(a) `1s` and `ls` (b) `ls ` and `2p_(x)`
(c ) `2p_(y)` and `2p_(y)` (d) `2p_(x)` and `2p_(y)`
(e) `1s` and `2s` .`

Explanation

To determine which pairs of orbitals will form a sigma bond, we need to understand the conditions for sigma bond formation. Sigma bonds are formed through head-on (axial) overlapping of orbitals. Let's analyze each option step by step:

### Step-by-Step Solution:

1. **Option (a): `1s` and `1s`**
- **Analysis**: Both are `s` orbitals. `s` orbitals can overlap directly along the inter-nuclear axis (the x-axis in this case).
- **Conclusion**: This pair will form a sigma bond.

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