Which operation is not closed for polynomials ?

Dividing two binomials will not always result in a polynomial. For instance, divide (x+2) over (x+3) and we won't get a polynomial. The result is known to be a rational expression but not a polynomial. So that's why division is not closed for polynomials.

Contrast that with addition, subtraction and multiplication. For any of those operations taking two polynomials and adding them, subtracting them, or multiplying them will lead to another polynomial. That's why these operations are closed for polynomials.

Choice B