To determine the correct mirror image of the given figure when the mirror is placed at MN, we need to follow these steps:

1. Understand Mirror Images: In a mirror image, the orientation along the axis perpendicular to the mirror flips, while the distance of each element from the mirror remains the same.
2. Analyze the Original Image: The given image is a sequence of letters with the mirror placed to the right.
3. Create the Mirror Image: When each letter is mirrored, it flips horizontally. Any letter consisting of vertical elements, like those with vertical symmetry (A, H, I), remains relatively unchanged concerning orientation, while others flip.
4. Select the Correct Option: Visually compare the options and determine which mirror reversal matches the properties discussed. The correct mirror image should display the original figure flipped as such:

Conclusion: After analyzing the provided options, the correct answer is the one mirrored correctly according to the MN line, maintaining relative positioning and flipping horizontally.