(a) Alluvial Soil — Consist of sand and silt is correctly matched. Alluvial soils are made up of sand, silt, and clay deposited by rivers.
Options (b), (c), and (d) are incorrect: Black soil has high moisture-retaining capacity (not high salt content); Arid soil has diffusion of iron giving it a red colour; Laterite soil is formed by intensive leaching — it is not made up of lava flows (that describes Regur/Black soil). Option (a) is the only correct match as alluvial soils are indeed composed of sand, silt, and clay.