Which of these is an effective method to secure a ladder when working on it?

Securing a ladder at the top is an effective method to ensure stability and safety while working. When a ladder is secured at the top, it minimizes the risk of slipping or falling over, especially if it is extended or used at a significant height. This technique helps to provide additional support, making the ladder more reliable and reducing the potential for accidents.

In contrast, other methods can introduce risks. For example, leaving a ladder unguarded does not provide any support or security and increases the chance of it being moved or falling. While bracing a ladder against a wall may seem stable, it can only be effective to a certain extent and may not account for side-to-side movement if the ladder isn't properly secured. Using ropes at the base can help provide stability but may not offer the same level of security as securing it at the top. Thus, securing a ladder at the top is a proactive approach that enhances safety during the task.