Select the odd word in the group : Book, Paper, Pencil, Pen, Eraser

Concept. A valid odd-one-out rule places all but one member in the same functional class. For an object-use list, define the class narrowly and test every word by the same criterion; a trial rule that excludes two or more members cannot identify a unique odd word.

Application to this group.

1. List the words to be tested: Book, Paper, Pencil, Pen, Eraser.

2. Use one consistent class: a loose writing surface, a mark-making implement, or an erasing aid used directly while writing or drawing.

3. Paper supplies the loose surface; a pencil and a pen make marks; an eraser removes pencil marks. Each participates directly in creating or correcting writing or drawing.

4. A book is a bound publication whose pages form a finished text read as a unit. It is not the loose surface, mark-making implement, or erasing aid described by the class.

5. The same criterion therefore includes Paper, Pencil, Pen and Eraser and isolates Book, so the odd word is Book.

Cross-check against rival rules.

• The rule “is made of paper” includes Book and Paper but excludes Pencil, Pen and Eraser, so it produces three outsiders rather than one.

• The rule “makes marks” includes only Pencil and Pen; it excludes Paper, Book and Eraser, so it also fails the one-outsider test.

• Book is itself one of the offered single-word values, and the consistent functional rule isolates only that value. Thus neither a multiple-outlier choice nor a none-of-the-offered-values choice is needed.

Result: Book.