In the given diagram:
I. Rectangle represents persons who know English.
II. Triangle represents persons who know Marathi.
III. Square represents persons who know Telugu.
IV. Circle represents persons who know Hindi.
The regions labelled from 1 to 12 represent various combinations of language proficiency among the individuals.

How many individuals can speak English exclusively?

To find the number of individuals who can speak English exclusively, we need to locate the region that lies only within the rectangle (representing English) and does not overlap with any other geometric shape (triangle, square, or circle).
Looking at the diagram:

* The rectangle represents English.
* The region labeled with the number $12$ lies completely inside the rectangle but outside the triangle, square, and circle.

Therefore, $12$ individuals can speak English exclusively.