- The order is the highest derivative present: here, $\frac{d^2 y}{dx^2}$. So, Order = 2.
- The degree is the power of the highest order derivative after making it free from radicals or fractions: here, $\Big( \frac{d^2 y}{dx^2} \Big)^2$, so Degree = 2.
- Difference = Order - Degree = 2 - 1 = 1.
Wait! There is a mistake here — the degree is the exponent of the highest order derivative:
\[
\Big( \frac{d^2 y}{dx^2} \Big)^2 \implies \text{Degree} = 2.
\]
So,
\[
\text{Difference} = 2 - 2 = 0.
\]
So, final answer: (D) 0.