In this riddle, what is black when it is clean and white when it is dirty?

Introduction / Context:
This riddle plays with our expectations about cleanliness. Most objects become darker, stained or dull when they are dirty and lighter or clearer when they are clean. Here, the situation is reversed, which hints that we are dealing with something that is naturally dark but turns light when covered by chalk or writing. The chalkboard, also called a blackboard, is a classic answer that fits perfectly with this unusual description.

Given Data / Assumptions:

• The object is black in its clean state.
• The same object appears white when it is dirty.
• Options include Shoes, Car, Chalkboard, None of these and Black shirt.
• We assume dirty means covered with the substance it is normally used with.

Concept / Approach:
The key is to remember how chalkboards are used. A clean chalkboard is dark, usually black or deep green, with a smooth empty surface. When a teacher writes on it with white chalk, the chalk dust and marks cover the board. In that condition, the board is functionally dirty yet looks white or covered with white writing. None of the other listed objects regularly switch from black when clean to white when in use in such a logical way.

Step-by-Step Solution:
Step 1: Understand that clean for this object means no extra material on its surface. Step 2: Recognise that chalkboards, when unused and freshly cleaned, are typically black or dark green. Step 3: When chalk is used heavily, the surface becomes coated with white or light coloured chalk dust. Step 4: This dusty state can be described as dirty, because the board needs to be wiped to return to its original condition. Step 5: Observe that in this dirty state, the board appears white or very light due to the chalk, exactly matching the riddle. Step 6: Compare this behaviour with shoes, cars or shirts, which usually become darker or stained when dirty, not white.

Verification / Alternative check:
Try applying the description to each listed object. Shoes and cars may show dust, but they come in many colours and typically do not shift from black when clean to white when dirty as a standard pattern. A black shirt covered with lint may look lighter, but this is not a common standard riddle answer. On the other hand, blackboard riddles are very popular in clever question sets, and the clean black and dusty white appearance is widely recognised. This confirms Chalkboard as the best and intended answer.

Why Other Options Are Wrong:
Shoes: They can be any colour and usually look worse when dirty, but not specifically white.
Car: A dark car may look dusty, yet the change is not a classic clean black, dirty white transformation.
None of these: This is incorrect because Chalkboard clearly fits both parts of the description.
Black shirt: It may catch lint, but the riddle is not traditionally about clothing and this choice is less precise.

Common Pitfalls:
Many learners first think about objects that change colour dramatically when washed or stained, which leads them to guess clothes or vehicles. The trick is to focus on something that is intentionally written on and repeatedly cleaned. Once you recall that chalkboards start dark and become white with chalk coverage, the riddle becomes straightforward. Practice with similar word puzzles will train you to look for typical school or classroom objects when such clues appear.

Final Answer:
The object that is black when clean and white when dirty is a Chalkboard or blackboard.