The microrelief of soils produced by expansion and contraction with changes in moisture is known as:

✅ Explanation:
-Gilgai is a distinctive microrelief pattern on the soil surface characterized by mounds and depressions. It forms due to the shrinking and swelling of clay-rich soils in response to changes in moisture content.
-The expansion and contraction of clay minerals cause the soil to crack and heave, creating the uneven surface.

📌 Other Options Explanations:
-Option A: Fluvial deposits: Fluvial deposits are sediments transported and deposited by rivers. They typically form larger landforms like floodplains and deltas.
-Option C: Mottling: Mottling refers to the variegated color patterns in soil caused by the presence of both oxidized (reddish-brown) and reduced (grayish) iron compounds. It's often an indicator of fluctuating water tables.
-Option D: Heaving: Heaving is the upward movement of soil or rock due to freezing and thawing or other processes. While it can create some surface unevenness.