Introduction:
The given statements are related to the spacing and strain requirements for longitudinal reinforcement in concrete structures made with different grades of steel. Let's evaluate each statement separately to determine their correctness.

Statement i: The minimum spacing required for the longitudinal reinforcement increases as the grade of steel increases.

Explanation:
The spacing of longitudinal reinforcement bars in reinforced concrete structures is governed by several factors, including the grade of steel. The spacing requirements are specified to ensure adequate bond strength between the reinforcement and the surrounding concrete, as well as to control cracking and ensure proper load transfer.

When the grade of steel increases, it generally means that the steel has higher strength. Higher strength steel can resist higher stresses and strains before yielding or failing. Therefore, the minimum spacing required between reinforcement bars can be reduced because the higher strength steel can effectively transfer higher loads without excessive deformation or failure.

On the other hand, if the grade of steel decreases, the minimum spacing required between reinforcement bars must be increased to ensure sufficient load transfer capacity and prevent premature failure.

Based on the above explanation, it is evident that statement i is incorrect. The minimum spacing required for longitudinal reinforcement decreases as the grade of steel increases, not increases.

Statement ii: Less strain is required due to the high grade of steel.

Explanation:
Strain is a measure of deformation in a material due to applied stress. In reinforced concrete structures, the strain in the longitudinal reinforcement depends on the applied loads and the properties of the steel, including its grade.

When high-grade steel is used in reinforced concrete structures, it typically has higher yield strength and ultimate tensile strength. This means that the steel can withstand higher stress levels before yielding or failing.

Since strain is directly proportional to stress, higher strength steel will require less strain to reach its yield point or ultimate tensile strength. In other words, the high-grade steel can undergo less deformation (strain) to resist the applied loads.

Therefore, statement ii is correct. Less strain is required due to the high grade of steel.

Conclusion:
From the analysis, we can conclude that only statement ii is correct, while statement i is incorrect. The minimum spacing required for longitudinal reinforcement decreases as the grade of steel increases, and less strain is required due to the high grade of steel.