The question "Which object is chair?" seems to be asking for an identification or clarification regarding what constitutes a chair. To answer this, we need to define what a chair is and then identify which object among a given set fits that definition. Since no specific objects are provided in the question, I will provide a general explanation of what a chair is and how to identify one.

What is a Chair?

A chair is a piece of furniture designed to provide a seat for one person. It typically consists of a seat, a backrest, and sometimes armrests. Chairs are commonly used in homes, offices, schools, and various other settings. They come in a wide variety of styles, materials, and designs, ranging from simple wooden chairs to elaborate, upholstered armchairs.

Key Features of a Chair

1. Seat: The seat is the horizontal surface where a person sits. It is usually flat or slightly contoured for comfort.
2. Backrest: The backrest is the vertical surface that supports the back of the person sitting in the chair. It can vary in height and shape.
3. Legs: Chairs typically have four legs, although some designs may have fewer or more. The legs support the seat and elevate it above the ground.
4. Armrests: Some chairs have armrests, which are horizontal surfaces on either side of the seat where a person can rest their arms.
5. Material: Chairs can be made from various materials, including wood, metal, plastic, and fabric.

Identifying a Chair

To identify a chair among a set of objects, look for the key features mentioned above. Here are some steps to follow:

1. Look for a Seat: Identify an object with a flat or slightly contoured surface that is designed to support a person's weight when sitting.
2. Check for a Backrest: Ensure that the object has a vertical surface behind the seat to support the back.
3. Count the Legs: Most chairs have four legs, but some may have three or more. Ensure that the object has legs that elevate the seat above the ground.
4. Look for Armrests: If the object has armrests, it is more likely to be a chair, although not all chairs have armrests.
5. Consider the Material: Chairs can be made from various materials, so the material alone is not a definitive indicator, but it can help in identifying the type of chair.

Examples of Chairs

1. Dining Chair: A simple chair with a seat, backrest, and four legs, typically used at a dining table.
2. Armchair: A chair with armrests, often upholstered for added comfort.
3. Folding Chair: A portable chair that can be folded for easy storage and transport.
4. Recliner: A chair with a backrest that can be tilted back and a footrest that extends, allowing the user to recline.
5. Stool: A simple seat without a backrest, often used in bars or as a footrest.

Conclusion

In summary, a chair is a piece of furniture designed for sitting, characterized by a seat, backrest, and legs. To identify a chair among a set of objects, look for these key features. Without specific objects to compare, the general definition and characteristics of a chair should help you recognize one when you see it.

If you have a specific set of objects in mind and need help identifying which one is a chair, please provide more details, and I can assist further.