**Core Concept**
The minimum angle of resolution (MAR) is the smallest angle between two points that a person with normal vision can distinguish. It is a measure of visual acuity and is typically expressed in minutes of arc.

**Why the Correct Answer is Right**
The minimum angle of resolution is 1 minute of arc for a person with 6/6 visual acuity. This is because a person with normal vision can distinguish two points that are 1 minute of arc apart. This is equivalent to being able to see two points that are 0.05 mm apart at a distance of 6 meters. The human eye has a remarkable ability to resolve small angles, and this is due to the structure of the retina, particularly the arrangement of photoreceptors in the fovea.

**Why Each Wrong Option is Incorrect**
**Option B:** 5 minutes of arc is incorrect because it is a larger angle than the minimum angle of resolution, and a person with 6/6 visual acuity would not be able to distinguish two points that are 5 minutes of arc apart.

**Option C:** 10 minutes of arc is incorrect because it is an even larger angle than 5 minutes of arc, and a person with 6/6 visual acuity would not be able to distinguish two points that are 10 minutes of arc apart.

**Option D:** 15 minutes of arc is incorrect because it is a very large angle, and a person with 6/6 visual acuity would not be able to distinguish two points that are 15 minutes of arc apart.

**Clinical Pearl / High-Yield Fact**
It's worth noting that the minimum angle of resolution can vary depending on the distance between the two points, and it can also be affected by factors such as the size of the pupil and the presence of any ocular pathology.

**✓ Correct Answer: A. 1 min of arc**