A period is the time required for half of the atoms of a radioactive element to decay

Radioactive Decay – Measuring the Age of the Solar System The half-life of a radioactive element is the amount of time it takes for half of the atoms in a sample to decay from an unstable state to a stable one.

Explanation:

white blood cells or wbc s are mainly 2 types-

1.agranulocytes

2.granulocytes

the monocytes or macrophages of agranulocytes , dendritic cells which are accessory leucocytes, and b cells which is one type of lymphocytes   identify the antigens present on the pathogen's surface. these three cells are called antigen presenting cells(apc) which are phagocytes and destroy the antigens by secreting antitoxins. besides this leukocyte is always plays vital role in the immunity of the body.

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