46.Radioactive disintegration of uranium ultimately results in formation of

47.Which one of the following is the petroleum wax ?

48.Which of the following statements are correctly associated with ultrasonic waves ? 1. These are the acoustic waves of frequencies more than 20,000 Hertz. 2. When possible to use, these waves are preferred over X-rays for getting an image of internal organs because they are not harmful. 3. Their velocity is more than the velocity of sound.

49.Old - written material, which cannot be read easily, can be read by

50.Consider the following statements : 1. Gamma rays are not constituents of nuclei but they are emitted when a nucleus in an excited state returns to its normal state. 2. The neutron to proton ration for stable nuclei is always less than one. 3. Beta rays consist of ordinary electrons which are of nuclear origin but do not revolve in orbits. 4. Both X - rays and gamma rays are electromagnetic radiations.