The threshold for inducing ventricular fibrillation, a life-threatening condition where the heart quivers instead of pumping blood effectively, is typically around 75 milliamps (mA) when applied to the human body for a brief duration. This level of current within that time frame is critical because it can disrupt the normal electrical impulses that regulate heart rhythm.
While 50 mA may induce other effects such as muscle contractions or pain sensations, it is generally not sufficient to cause ventricular fibrillation in the majority of individuals. Similarly, 100 mA for 2 seconds might indeed be dangerous but could also lead to immediate severe burns or other injuries, which complicates the physiological factors at play. On the other hand, 25 mA for 15 seconds is below the threshold generally recognized for causing such a severe cardiac condition.
Hence, the option that specifies 75 mA for 5 seconds aligns with established data on the effects of electric shock on the human heart, making it the correct choice. Understanding the range of current that can result in serious arrhythmias is crucial for safety in environments where electrical work is performed.