How old is a radioactive specimen if the half-life is 5,000 years and only 12.5% of the original material is remaining? 20,000 years 15,000 years 10,000 years 5,000 years

During the refrigeration cycle, what does the refrigerant do? absorbs and releases thermal energy by first vaporizing then condensing. absorbs and releases thermal energy by first condensing then vaporizing. insulates the thermal energy away from the cooling area. transfers thermal energy to the cooling area by condensing.