The order of a differential equation is determined by the highest derivative of the unknown function. In this case, the given equation is:
\[
\frac{d^2y}{dx^2} - 6x = 3x^4 - 2x^3 + 2
\]
The highest derivative in this equation is \(\frac{d^2y}{dx^2}\), which is the second derivative of \(y\). Therefore, the order of the differential equation is 2.
Thus, the correct answer is (B).