Series-parallel resistance in cuboid assembly

Steps:

• Cuboid is 1×2×5 cubes; assume X and Y are opposite 1×2 faces (ends of 5-cube dimension).
• Each cross-section has 2 cubes in parallel: equivalent resistance = 4Ω / 2 = 2Ω.
• Five such cross-sections connect in series along the 5-unit length.
• Total resistance = 5 × 2Ω = 10Ω.

Why C is correct:

• Series-parallel combination formula (1/Req = sum(1/Ri) for parallel, Req = sum(Ri) for series) gives exactly 10Ω.

Why the others are wrong:

• A. 1.6Ω: Incorrect parallel miscalculation, like assuming more than 2 paths.
• B. 2.0Ω: Resistance of single cross-section only, ignoring series connection.
• D. 40Ω: Treats all 10 cubes as series, ignoring parallel paths.

Final answer: C