Redshift measures recession speed and distance via Hubble's law

Steps:

• Redshift (z) quantifies light stretching from Doppler effect due to recession.
• Smaller z for X than Y means X recedes slower than Y.
• Hubble's law (v = H₀d) links recession velocity v (from z ≈ v/c for low z) to distance d.
• Thus, slower v for X implies smaller d; faster v for Y implies larger d and faster recession.

Why B is correct:

• B matches Hubble's law: smaller z for X means closer to Earth and slower recession; larger z for Y means faster recession.

Why the others are wrong:

• A: X recedes slower, not faster.
• C: Y has larger z, so farther, not closer.
• D: Y is farther, not closer.

Final answer: B