1. Identify the geometry

A square planar complex has four ligand positions lying in the same plane, oriented along the $x$ and $y$ axes.

2. Required hybridisation for square planar geometry

The hybridisation used for square planar complexes is:

$dsp^2$

This involves mixing:

• one $s$ orbital,
• two planar $p$ orbitals: $p_x$ and $p_y$,
• one $d$ orbital oriented along the $x$ and $y$ axes.

3. Choose the correct $d$ orbital

For square planar bonding, the metal-ligand bonds lie along the $x$ and $y$ axes. The $d$ orbital that has lobes directed exactly along these axes is:

$d_{x^2-y^2}$

So the set of orbitals is:

$s,\ p_x,\ p_y,\ d_{x^2-y^2}$

4. Check options

• A: $s, p_x, p_y, d_{xy}$ → incorrect, because $d_{xy}$ lies between the axes.
• B: $s, p_x, p_y, d_{x^2-y^2}$ → correct.
• C: $s, p_x, p_y, d_{z^2}$ → incorrect for square planar hybridisation.
• D: $s, p_x, p_y, d_{yz}$ → incorrect, not oriented in the square plane for this purpose.

5. Final answer

The square planar complex is formed by hybridisation of:

$s,\ p_x,\ p_y,\ d_{x^2-y^2}$