ANS:D - 25 mm

The minimum thickness of the cover at the end of a reinforcing bar is crucial for ensuring proper concrete protection and durability of the reinforcement. It helps prevent corrosion and provides adequate bond strength between the reinforcement and the surrounding concrete. Among the options provided, the minimum thickness of the cover at the end of a reinforcing bar should not be less than twice the diameter of the bar or a minimum of: 25 mm This requirement ensures sufficient concrete cover to adequately protect the reinforcement bar, even at its end, where vulnerability to corrosion and mechanical damage is typically higher. Adequate concrete cover is essential for the long-term performance and durability of reinforced concrete structures. Therefore, the correct option is: 25 mm