Final answer:
The half-life of a substance is calculated by the time it takes for half of it to decay. Based on the scenario where a sample goes from 200 grams to 5 grams in 50 years, it would require more than four half-lives, but without more precise data, a specific value cannot be determined. It's important to note that oxygen is stable and does not decay in the manner described in the question.
Step-by-step explanation:
To determine the half-life of a substance, we need to calculate the time it takes for half of the initial amount to decay or change. If we begin with a 200-gram sample of a substance that decays to 5 grams in 50 years, we can use the process of halving to find out the half-life duration. This means that the initial 200 grams become 100 grams after one half-life, 50 grams after two half-lives, 25 grams after three half-lives, and finally reaching 12.5 grams after four half-lives. To decay down to 5 grams, it would take slightly more than four half-lives. However, the information provided in the question seems incorrect as oxygen does not decay in this manner, suggesting a possible misinterpretation of the original question scenario.
Nevertheless, if we were to follow the decay pattern described since we can determine it took approximately 50 years for the sample to be reduced from 200 grams to 5 grams, we could divide these 50 years by the number of half-lives we approximated (more than four) to get an estimate of the half-life. This is not a typical calculation for oxygen, as again, oxygen is stable and does not undergo such decay, and the exact number of half-lives in the given scenario isn't specified, it is not possible to provide a precise answer based on the information provided.