Which of the following is a characteristic of a good padlock?

A good padlock is characterized by its security features, and one key feature is the five pin tumbler mechanism. This design enhances the lock's resistance to picking, which is a common method of bypassing security. The use of a five pin tumbler system makes it more complex than standard locks, which generally have fewer pins. This increased complexity requires a more sophisticated key and makes unauthorized access significantly more difficult.

Other characteristics such as lightweight design, bright color, and plastic casing do not directly contribute to the effectiveness and security of a padlock. While a lightweight design may be convenient for portability, it can also suggest that the lock is made from weaker materials. A bright color may make a padlock more visually appealing, but it does not impact security. Likewise, a plastic casing may be less durable and not provide the same level of protection as a metal casing, which is generally preferred for securing valuables. Thus, the five pin tumbler mechanism stands out as a fundamental characteristic that directly contributes to the security level of the padlock.