Geometrical isomers are different spatial arrangements of the atoms or groups in a molecule. In the given complex [MA2(D)2], A is unidentate, meaning it can form a single bond with the central metal atom, while D is didentate, meaning it can form two bonds with the central metal atom.

To determine the number of geometrical isomers, we need to consider the possible arrangements of the ligands A and D around the central metal atom.

There are two A ligands, which can be arranged in two different ways:
1. A ligands on opposite sides of the central metal atom (trans configuration)
2. A ligands on the same side of the central metal atom (cis configuration)

Similarly, there are two D ligands, which can also be arranged in two different ways:
1. D ligands on opposite sides of the central metal atom (trans configuration)
2. D ligands on the same side of the central metal atom (cis configuration)

To find the total number of geometrical isomers, we need to consider all possible combinations of the A and D ligands.

Possible combinations:
1. trans-A, trans-D
2. trans-A, cis-D
3. cis-A, trans-D
4. cis-A, cis-D

From the above combinations, we can see that there are two possible geometrical isomers: trans-A, trans-D and cis-A, cis-D.

Hence, the correct answer is option 'B' which states that there are 2 geometrical isomers possible in a complex of type [MA2(D)2], where A is unidentate and D is didentate.