<Two friends arguing>
Arjun: If a figure can be folded along any line such that one half superimposes the other, it is known as symmetric figure.
Shubh: If you can find a line in the figure which divides it in identical parts, then the figure is always symmetric.
Arjun is right and Shubh is wrong
If a figure can be folded along any line such that one half superimposes or aligns exactly with the other, it is known as symmetric figure.
For example: If you take a square and fold it across the line shown, part 1 exactly overlaps part 2. So, square is a symmetric figure.
On the other hand, in a parallelogram, the diagonal divides it into two congruent triangles (can be proven using SSS congruence condition), i.e. into two equal parts. But those parts don’t superimpose each other when folded across diagonal (as shown in the figure). So, parallelogram is not symmetric.
Hence, Arjun is right and Shubh is wrong.