Answer:
To determine which of the given equations is not a quadratic equation, we need to understand what a quadratic equation is.

Quadratic Equation:
A quadratic equation is a polynomial equation of degree 2, which means the highest power of the variable is 2. It can be written in the form ax² + bx + c = 0, where a, b, and c are constants and a ≠ 0.

Now, let's analyze each option to determine if it is a quadratic equation:

(a) x² + 3x - 5 = 0:
This equation is a quadratic equation because it is in the form ax² + bx + c = 0, where a = 1, b = 3, and c = -5.

(b) x² + x³ + 2 = 0:
This equation is not a quadratic equation because it contains a term with a degree higher than 2. The term x³ makes it a cubic equation, not a quadratic equation.

(c) 3 + x + x² = 0:
This equation is a quadratic equation because it is in the form ax² + bx + c = 0, where a = 1, b = 1, and c = 3.

(d) x² - 9 = 0:
This equation is a quadratic equation because it is in the form ax² + bx + c = 0, where a = 1, b = 0, and c = -9.

Conclusion:
Among the given options, option (b) x² + x³ + 2 = 0 is not a quadratic equation because it contains a term with a degree higher than 2. The other options (a), (c), and (d) are all quadratic equations.