यदि किसी रेडियोधर्मी पदार्थ को अपनी प्रारंभिक सक्रियता के 88% से घटकर 77% होने में 12 मिनट का समय लगता है, तो उस पदार्थ का अर्ध-आयु काल (half-life) मिनटों में लगभग कितना होगा?

Four statements regarding nuclear properties are given (where A is the mass number): A. The volume of a nucleus is proportional to A1/3. B. The volume of a nucleus is proportional to A. C. The difference in mass of an atom and its nucleus is called the mass defect. D. The difference in mass of a nucleus and its constituent nucleons is called the mass defect. Choose the correct answer from the options given below:

Which of the following is used as a moderator in a nuclear reactor?