4. If a radioactive substance has a half life of 5.0 minutes, which of the following statements is correct? 1. it will take at least 5.0 minutes for the raction to begin 2. at the end of 5.0 minutes, the amount of radioactive material will have doubled. 3. At the end of 10.0 minutes, the amount of radioactive material will be 1/4th as much as originally present 4. At the end of 5.0 minutes, the amount of radioactive material will have tripled. 5. The law of conservation of energy states that in the absence of external work input or output________. 1. energy cannot be created or destroyed 2. mass cannot be created or destroyed 3. momentum cannot be created or estroyed 4. energy can b created and then destroyed