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

Concept. A classification (odd-one-out) item is decided by one governing property, never by a general impression. Choose a property, test it against every word in the group, and keep it only if it is true of all the words but exactly one. The single word for which that well-supported property fails is the odd word.

Applying it to this group.

1. Write out the group: Book, Paper, Pencil, Pen, Eraser.

2. Propose a property: "is a stationery article handled in the act of writing or drawing".

3. Test it on Paper, Pencil, Pen and Eraser: paper is the surface the marks are made on, a pencil and a pen are the implements that make the marks, and an eraser is the article that lifts them off. The property is true of all four.

4. Test it on the remaining word: a book is a bound set of printed pages issued as a publication and read as finished text, so it is neither an implement nor a material consumed while writing. The property fails for it.

5. The property therefore holds for exactly four of the five words and fails for exactly one, so the odd word is Book.

Cross-check against rival properties.

• "Is made of paper" is true of Book and Paper but false of Pencil, Pen and Eraser. It fails for three words, so it isolates no single outsider.

• "Puts marks on a surface" is true only of Pencil and Pen, because paper and a book do not mark anything. This is why an eraser cannot be split off on the ground that it removes marks instead of making them: the mark-making property already fails for two other words in the group.

• Since exactly one word is isolated and that word is present in the group, the group does not contain two equally odd words.

Answer: Book. The official BPSC answer key for General Studies Paper 2 of 24 August 2023 (1st sitting) also marks Book as the answer, and the standard published explanation is the same one used above: paper, pencil, pen and eraser are all used directly in writing or drawing.