The correct option is A Region (i)
Rusting takes place in the presence of air and moisture. Among the given regions, region (ii) is a desert where the moisture content in air will be too low. In region (i) and (iii) the air and moisture content are quite high. However, salt water in the coastal region (i) increases the rate of rusting. So, it is region (i) where the rusting will be the fastest.