The correct answer is option 'B' - Vaseline.

Explanation:

Shrinkage Dish:
A shrinkage dish is a device used to measure the drying shrinkage of cementitious materials. It consists of a circular metal dish with a diameter of 100 mm and a depth of about 10 mm. The dish is made of non-reactive material, typically stainless steel, to prevent any chemical reactions with the test material.

Coating the Inside:
The inside of the shrinkage dish needs to be coated with a thin layer of a substance to prevent the test material from sticking to the dish during the drying process. This coating ensures that the shrinkage of the test material is not influenced by any adhesion to the dish.

Vaseline:
Vaseline, also known as petroleum jelly, is commonly used to coat the inside of the shrinkage dish. It is a semi-solid mixture of hydrocarbons derived from petroleum. Vaseline has several properties that make it suitable for this purpose:

1. Non-reactive: Vaseline does not react with cementitious materials or any other substances commonly tested in the shrinkage dish. This ensures that the test results are not affected by any chemical reactions between the coating and the test material.

2. Non-absorbent: Vaseline is non-absorbent, meaning it does not absorb moisture from the test material or the surrounding environment. This helps to maintain the integrity of the test and prevent any changes in the moisture content of the test material.

3. Easy application: Vaseline can be easily applied to the inside of the shrinkage dish using a brush or a cloth. Its semi-solid consistency allows for a thin and uniform coating, ensuring that the test material does not adhere to the dish.

4. Easy removal: After the test is complete, any remaining Vaseline can be easily removed from the shrinkage dish using a cloth or a cleaning agent. This allows for repeated use of the dish without any residual effects from previous tests.

In conclusion, the inside of the shrinkage dish is coated with a thin layer of Vaseline to prevent the test material from sticking to the dish during the drying process. Vaseline is non-reactive, non-absorbent, easy to apply, and easy to remove, making it an ideal choice for this purpose.