Find the image of △ 𝐴𝑂𝐵 after 90° anticlockwise rotation about O.

The correct answer is: △ 𝐴𝑂𝐵 → △ BOC

First try to turn the given figure through given angle towards left and notice which new vertex is has taken place of the original vertex.
We will notice that when the given figure is rotated 90° anticlockwise A → B and B → C and O → O
So, △ 𝐴𝑂𝐵 → △ BOC
( keep order in which triangle is defined in mind)