The correct answer is option 4. The cost of producing iron in India is lower than in other countries because coal and iron ore are found in the same area. This proximity reduces transportation costs and makes it more cost-effective to extract and process iron.

Option 1, low wage of miners, might contribute to cost savings, but it is not the primary reason for the lower cost of iron production in India compared to other countries.

Option 2, a large supply of iron ore, is an important factor, but it alone does not explain the lower cost. Other countries also have abundant iron ore reserves, but the cost of production may still be higher due to transportation and logistical challenges.

Option 3, a large supply of coal, is also a significant factor, but it does not provide a complete explanation for the lower cost. The close proximity of coal and iron ore deposits in the same area is the key advantage that reduces costs in India.

Therefore, option 4 is the best explanation for the lower cost of iron production in India.