which of the following things would not fit in una mochila?\no una silla\no un borrador\no un cuaderno\no…

Brief Explanations:

"una silla" means a chair which is large and cannot fit in a backpack ("una mochila"). "un borrador" (an eraser), "un cuaderno" (a notebook), and "una pluma" (a pen) are small enough to fit in a backpack.

Answer:

una silla