ANS:C - < 1

The steam economy in a single-effect evaporator system refers to the ratio of the mass of vaporized water to the mass of steam used in the process. In a single-effect evaporator system, the steam economy is typically less than 1. This means that the amount of vaporized water produced is less than the amount of steam consumed. This inefficiency occurs due to heat losses, inefficiencies in the heat transfer process, and other factors. So, the correct answer is: "< 1"