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

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