Which of the following techniques is least effective in persuasion according to the content?

The correct choice indicates that "no technique" is considered the least effective in persuasion because persuasion relies heavily on the use of specific techniques to influence an audience. When no persuasive technique is employed, there is a lack of structure or strategy, resulting in a failure to engage the audience or convey a message effectively.

Persuasion is fundamentally about communication, and without any technique, such as numbers, aesthetic appeal, or slogans, the message is likely to be vague or unconvincing. Each of the other techniques mentioned—numbers, aesthetic appeal, and slogans—has established effectiveness in engaging audiences and reinforcing arguments, while the absence of any technique means there is no means to persuade at all.

In summary, effective persuasion requires a purposeful approach, and not using any technique minimizes the chance of achieving the desired influence on an audience.