Explanation:

The maximum number of 90 angles between bond pair-bond pair of electrons is observed in sp3d2-hybridisation.

In order to understand this, let's first understand what hybridisation is.

Hybridisation:

Hybridisation is a concept used to explain the structure of molecules. It is the mixing of atomic orbitals to form new hybrid orbitals that are responsible for the bonding in molecules.

The hybrid orbitals have different shapes, energies and orientations than the atomic orbitals from which they are formed.

Types of Hybridisation:

There are several types of hybridisation, such as sp, sp2, sp3, sp3d, sp3d2, etc. The number of hybrid orbitals formed depends on the number of atomic orbitals that are hybridised.

Explanation of Options:

a) dsp3-hybridisation:

In dsp3-hybridisation, five orbitals are hybridised, including one d-orbital and three p-orbitals. This hybridisation results in five hybrid orbitals, which are arranged in a trigonal bipyramidal shape. However, there are only two bond pairs at 90 angles in this hybridisation.

b) sp3d-hybridisation:

In sp3d-hybridisation, six orbitals are hybridised, including one s-orbital, three p-orbitals and two d-orbitals. This hybridisation results in six hybrid orbitals, which are arranged in an octahedral shape. However, there are only four bond pairs at 90 angles in this hybridisation.

c) dsp2-hybridisation:

In dsp2-hybridisation, four orbitals are hybridised, including one d-orbital and two p-orbitals. This hybridisation results in four hybrid orbitals, which are arranged in a square planar shape. However, there are only two bond pairs at 90 angles in this hybridisation.

d) sp3d2-hybridisation:

In sp3d2-hybridisation, seven orbitals are hybridised, including one s-orbital, three p-orbitals and three d-orbitals. This hybridisation results in seven hybrid orbitals, which are arranged in a pentagonal bipyramidal shape. There are six bond pairs at 90 angles in this hybridisation, which is the maximum number of bond pairs at 90 angles between bond pair-bond pair of electrons.

Conclusion:

Hence, we can conclude that the correct option is (d) sp3d2-hybridisation, as it has the maximum number of 90 angles between bond pair-bond pair of electrons.