Plane mirror: reflection point at midpoint of eye and object heights

Steps:

• Image of shoes is at 0 cm behind mirror.
• Ray from eyes (150 cm) to shoe image (0 cm) intersects mirror at (150 + 0)/2 = 75 cm.
• Mirror must cover 75 cm to reflect this ray.
• For 50 cm length, lowest h satisfying h ≤ 75 ≤ h + 50 is h = 25 cm.

Why B is correct:

• Reflection occurs at midpoint height (75 cm) by plane mirror law; minimal h = 75 cm - 50 cm = 25 cm.

Why the others are wrong:

• A. 0: Top at 50 cm < 75 cm, misses reflection point.
• C. 50 cm: Works (covers 75 cm) but not smallest h.
• D. 75 cm: Works (just covers 75 cm) but not smallest h.

Final answer: B