Which everyday item is black when you buy it, red when you use it, and gray when you throw it away?

Introduction / Context:
This puzzle is a well known riddle that describes the changing appearance of a common object as it is used. Rather than asking directly for the name of the object, the riddle gives clues about its colour at three different stages: when bought, when used and when thrown away. The question tests lateral thinking and observation skills about everyday materials, especially those used for cooking or heating.

Given Data / Assumptions:
• The object is black when you buy it.
• It becomes red when you use it.
• It turns gray when you throw it away or after it has been completely used.
• The options are shoe, charcoal, clay pot and ink cartridge.
• We assume the riddle is referring to a single common item and not to a combination of things.

Concept / Approach:
The colour sequence black to red to gray is strongly associated with burning fuel. Charcoal is typically sold as black chunks. When charcoal is burning and very hot, it glows red. After it has burned out and cooled, it turns into gray ash. In contrast, shoes, clay pots and ink cartridges do not naturally follow this colour pattern during normal use. Therefore, mapping the three colour stages to the burning cycle of charcoal gives the correct answer.

Step-by-Step Solution:
Step 1: List the three colour states given in the riddle: black when bought, red when used, gray when thrown away. Step 2: Think of common things that are black when new. Shoes, charcoal and ink cartridges can all be black. Step 3: Now focus on the stage red when you use it. A shoe or ink cartridge does not usually turn bright red in normal use, but burning charcoal glows red hot. Step 4: Consider the final stage gray when you throw it away. Burned charcoal ends up as gray ash, which fits perfectly with this description. Step 5: Conclude that charcoal uniquely fits all three stages of the riddle in a natural way, so it must be the correct answer.

Verification / Alternative check:
To verify, imagine the life cycle of a piece of charcoal used in a traditional stove or barbecue. At the shop, charcoal pieces are fully black. During cooking, the pieces heat up and tiny glowing red areas appear as they burn. After cooking, when the fire dies and the material has been consumed, what remains is gray powder or fragile gray pieces of ash that are thrown away. This matches the riddle exactly. None of the other objects have such a clear three stage colour transformation in ordinary everyday use.

Why Other Options Are Wrong:
• Shoe: A shoe may be black when you buy it, but using it does not turn it red, nor does it naturally become gray in a consistent way when discarded.
• Clay pot: Clay pots are usually brown or red initially and may blacken with soot, but the three precise colours in the riddle do not match their normal use cycle.
• Ink cartridge: An ink cartridge may be black, but using it does not turn it red, and an empty cartridge stays mostly the same colour, not gray ash.

Common Pitfalls:
Some learners may focus only on the first colour black and quickly pick any black object they see in the options, such as a shoe, without carefully checking the later stages. Another pitfall is to think metaphorically about emotions or money instead of actual physical objects. For riddles like this, it helps to visualise the entire life cycle of an item from purchase through use to disposal, and then see which option fits all the described states.

Final Answer:
The object that is black when bought, red when used and gray when thrown away is charcoal.