The half life period of a radioactive substance is best determined by counting the number of alpha particles emitted per second in a Geiger Muller counter from its known quantity. If the half life period of a radioactive substance is one month, then

• 3/4th of it will disintegrate in two months.
• it will completely disintegrate in two months.
• it will completely disintegrate in four months.
• l/8th of it will remain intact at the end of four months.