• Forces on Gang of Disc Harrows:
• Assertion (A): Concave end of the disc harrow gang tends to penetrate more deeply than the convex end. $\implies$ True.
• The soil side forces acting on disc faces create a couple that tilts the gang, causing the outer concave end to dig in deeper while the convex end tends to ride out of the soil.
• Reason (R): The radial force, which includes the vertical support force on the disc blade, must pass slightly to the rear of the disc centerline. $\implies$ True.
• Due to soil resistance and forward travel velocity, the resultant radial reaction shifts slightly rearward of the vertical center axis.
• Relationship: Reason (R) describes longitudinal force line of action on an individual blade, but does not provide the causal explanation for gang-level moments across the width.
• Conclusion: Both (A) and (R) are true but (R) is NOT the correct explanation of (A) (Option 2).

Correct option: (2) Both (A) and (R) are true but (R) is NOT the correct explanation of (A).