Find the number of triangles in the given figure.

From first figure to second figure the outermost design is deleted while other two designs interchange positions.

Except in figure (4), in all other figures only two types of designs are given.

As we can see that figure (3) is different from the other three.
The lower line segment is inverted in figure (3).

All other figures have small opening. But figure (3) is different to others .

On the basis of above given question , we have
The mirror image always be opposite the original image across the given line MN. It will become opposite to the given line .As shown in given below .
Hence , option B is required answer .

Except figure (1), all other figures have five sides 1.

From first figure to second figure the design is inverted vertically.