Correct answer: 1000
According to Kepler's third law, the square of the orbital period (T) is proportional to the cube of the semi-major axis (r). Thus, (T₁/T₂)² = (r₁/r₂)³. Substituting r₁ = 10¹³ m and r₂ = 10¹² m, we get (T₁/T₂)² = (10¹³/10¹²)³ = 10³. Taking the square root, T₁/T₂ = 10^(3/2) = 1000. Hence, the ratio is 1000.