11.Activity of a radioactive material decreases to one third in 10 years. After 10 more years, final activity will be

12.Count rate of a GM count for the radiations of a radioactive material having half life of 30 minutes decrease to 5/sec in two hours. Then initial count rate of the material was

13.Energy of the first excited state of hydrogen atom is

14.Half life of an atom A is 2 days. If we start with 60,000 atoms of that material, number of atoms left over after 8 days will be

15.If the half of a radioactive material is 2 days at NTP, then on increasing the pressure to 16 atmospheres, new half life of the material will be