Okay, let's tackle this question. The question is about the age at which a child can walk alone. The options are missing, but the correct answer is supposed to be one of the options.

First, I need to recall the typical developmental milestones for motor skills in children. I remember that gross motor development follows a specific timeline. For walking, most children start to walk independently around 12 months. They usually take their first steps between 12 and 15 months.

The core concept here is the normal motor development in infants. The key point is the age when a child can walk without support. The correct answer should be 12-15 months.

Now, the options might include other ages like 9 months, 18 months, or 6 months. Let's think about each wrong option. For example, 9 months is when a child might start standing with support, but walking alone isn't expected yet. 18 months is well beyond the typical walking age, so that's incorrect. 6 months is too early; babies can't walk at that age.

The clinical pearl here is to remember the typical milestones: 6 months for sitting, 9 months for standing, 12 months for walking. That's a common sequence that's often tested.

So, putting it all together, the correct answer is 12 months. The explanation should cover the normal development timeline and why the other options are incorrect based on earlier or later milestones.

**Core Concept**
This question tests developmental milestones in pediatric motor skills. Independent walking without support typically occurs between 12 and 15 months due to the maturation of neuromuscular control, balance, and muscle strength.

**Why the Correct Answer is Right**
By 12 months, most children achieve the ability to walk independently. This milestone requires integration of vestibular input, proprioception, and motor cortex coordination. Key prerequisites include sitting unaided (6 months), crawling (9 months), and standing with support (10–12 months). The neuromuscular system matures sufficiently by this age to allow bipedal locomotion.

**Why Each Wrong Option is Incorrect**
**Option A:** 9 months—Incorrect. At 9 months, children typically sit independently and may cruise along furniture but cannot walk alone.
**Option B:** 6 months—Incorrect. At 6 months, infants are acquiring head control and rolling over; walking is impossible.
**Option C:** 18 months—Incorrect. While some children may walk by 18 months, this is well beyond the typical range and may indicate delayed development.

**Clinical Pearl / High-Yield Fact**
Remember the "6-9-12" rule for motor milestones:
- 6 months: Sits unaided
- 9 months: Stands with support
- 12 months: Walks independently
This sequence is critical for NEET PG/AIIMS questions on developmental delays.

**Correct Answer: D. 12 months**

✓ Correct Answer: A. 15 months