The normal range of breathing rate per minute in an average adult person at rest is option 2, which is 12 - 18 breaths per minute. This means that a healthy adult will take between 12 and 18 breaths every minute when they are not engaged in any physical activities or experiencing any stress. Option 1, which suggests 9-12 breaths per minute, is too low for a resting breathing rate. Option 3, which suggests 21-24 breaths per minute, is too high for a resting breathing rate. Option 4, which suggests 30-30 breaths per minute, is not a valid range as it provides the same number twice. It is important to note that these values can vary depending on factors such as age, activity level, and overall health.