Explanation:

- Option 1: Lime

- Correct Answer

- Blackboard chalk is commonly made from calcium carbonate, which is derived from limestone.

- It is a white, soft mineral found in nature.

- Option 2: Soft, sticky clay

- Chalk isn’t typically made from clay.

- Clay is used in ceramics and pottery, not for making educational chalk.

- Option 3: Remnant of petroleum

- Petroleum remnants are not used in chalk.

- Chalk doesn’t relate to petroleum products at all.

- Option 4: Raw form of calcium chloride

- Chalk is not made of calcium chloride.

- Calcium chloride is a salt and used for de-icing roads, not chalk production.