Which of the following overlaps is incorrect [assuming z-axis to be the internuclear axis]?
(P) `2p_(y)+2p_(y)rarrpi2p_(y)`
(Q) `2p_(z)+2p_(z)rarrsigma2p_(z)`
(R) `2p_(x)+2p_(x)rarrpi2p_(x)`
(S) `1s+2p_(y)rarrpi(1s-2p_(y))`

Options

A. P and Q
B. Q and S
C. Only S
D. none of these

Explanation

To determine which of the overlaps is incorrect, we need to analyze each option based on the principles of molecular orbital theory and the types of overlaps that can occur between atomic orbitals.

1. **Option (P): `2p_(y) + 2p_(y) → π2p_(y)`**
- The two 2p_y orbitals can overlap sideways (lateral overlap) to form a π bond. This overlap is correct.

2. **Option (Q): `2p_(z) + 2p_(z) → σ2p_(z)`**
- The two 2p_z orbitals can overlap end-to-end (axial overlap) to form a σ bond. This overlap is also correct.

3. **Option (R): `2p_(x) + 2p_(x) → π2p_(x)`**
- The two 2p_x orbitals can overlap sideways to form a π bond. This overlap is correct as well.

4. **Option (S): `1s + 2p_(y) → π(1s - 2p_(y))`**
- The overlap between a 1s orbital and a 2p orbital does not lead to a π bond. Instead, it can form a σ bond since the 1s orbital overlaps end-to-end with the 2p orbital. Therefore, this overlap is incorrect.

### Conclusion:
The incorrect overlap is **Option (S)**: `1s + 2p_(y) → π(1s - 2p_(y))`.