Step 1: Understanding the Concept:
For a cube of side \(L\) and mass \(M\), the density is \(\rho = \dfrac{M}{L^3}\). In the maximum error method, the percentage errors of the factors add up, each multiplied by the power of its quantity.
Step 2: Key Formula or Approach:
\[ \frac{\Delta\rho}{\rho} = \frac{\Delta M}{M} + 3\,\frac{\Delta L}{L} \]
Step 3: Detailed Explanation:
Given \(\dfrac{\Delta\rho}{\rho} = 8\%\) and \(\dfrac{\Delta M}{M} = 2\%\).
\[ 8 = 2 + 3x \Rightarrow 3x = 6 \Rightarrow x = 2\% \]
So the maximum error in the measurement of the length is 2 percent. Option (B) 4 % would need the density error to be 14 %. Option (C) 6 % and (D) 8 % ignore the power 3.
Final Answer:
The maximum error in length is 2 %, option (A).
\[ \boxed{2\% \text{ (A)}} \]