Out of the following which element has the longest half-life period?

A. Radium

B. Radon

C. Uranium-238

D. Plutonium

Please do not use chat terms. Example: avoid using "grt" instead of "great".

You can do it
  1. Rays similar to X-rays but of smaller wave length that are given off by radioactive substances are
  2. Formation of shadows can be explained by
  3. Out of the following which is an insulator?
  4. The velocity of sound in air increases with
  5. Photo-electric cells convert
  6. When a ship floats on water, the weight or water displaced is
  7. The period of a geostationary (synchronous) satellite orbiting the earth over the equator la
  8. The red colour of the setting sun is due to
  9. Water kept in an earthen pot is less cool on rainy days than in summer because during the rainy days
  10. Sound waves
  11. The sun continuously produces an enormous amount of energy. This la due to
  12. A thermostat is a device used
  13. Credit for starting Space Science Research in India goes to
  14. A radio set that uses valves does not start operating immediately when it is switched on whereas a set…
  15. Separating particles from a suspension is effected by
  16. The radiator in a car serves to
  17. A bar magnet tied in the middle with a thread is suspended at the South Pole of the earth. The magnet…
  18. A stone floor feels cold to the bare feet but a carpet on the same floor feels warm. This is because
  19. A temperature below absolute zero for an ideal gas
  20. Gamma radiations are used for
  21. The velocity of sound in air
  22. The completely dark portion of a shadow of an object is known as
  23. The largest planet in the solar system is
  24. Thick brick walls are used in the construction or a cold storage because bricks
  25. In compact porous soil, the rising of the water is due to
  26. The evaporation rate depends on
  27. Which of the following is wrongly matched?
  28. One finds it more difficult to walk on ice than on a concrete road because
  29. Where does the centre of gravity of a rubber ring lie?
  30. A rheostat is used