What is the first step in the process of corrosion attack?

The correct choice is based on the understanding of how corrosion initiates. Corrosion is a chemical process that primarily begins on the surface of the metal. This is because the metal's surface is where it comes into contact with environmental factors that can lead to corrosion, such as moisture, oxygen, and corrosive agents like salts.

Surface imperfections, such as scratches or microscopic cracks, can further expose more metal to humidity or pollutants, accelerating the corrosion process. Once the corrosion has established itself at the surface, it can propagate deeper into the metal structure.

Other options, while they may involve conditions related to corrosion, do not correctly identify the initial point of attack. For example, corrosion does not exclusively begin at joints or require specific alkaline conditions to initiate. Instead, these contexts may contribute to the severity or progression of the corrosion but are not the starting point of the attack.