Question

Which radioactive series do not show the formation of a radon atom as one of the intermediate?
A) ${\text{Th series}}$
B) ${\text{Np series}}$
C) ${\text{U series}}$
D) ${\text{Ac series}}$

Answer 1

Hint:The elements given here have unstable forms which emits ionizing radiation. So they keep transforming into different atoms (called decay products) until they reach a stable state and no longer emit radiation which forms a series. Here, Np series is the radioactive series in which the radon atom is not formed as one of the intermediate.

Step-by-Step Explanation:Elements of periodic table have unstable forms. These unstable forms produce ionizing radiation and thus are radioactive. This emission of energy is called radioactive decay. The unstable forms of element transform into a different atom called decay product. These atoms keep transforming until they reach a stable form and become balanced. The elements that decay in more than one step are called series. Each series has its own different and unique decay chain. The Neptunium series has following atoms present as decay products-actinium, astatine, bismuth, francium, lead, polonium, protactinium, radium, thallium, thorium and uranium. It has a unique trait of decay chain as it does not contain the noble gas radon as its decay product. Since the Np series does not have radon its decay chain does not migrate through rocks as much as the decay chain of thorium, uranium and actinium do.
Hence the correct answer is ‘B.’
Note: Although most elements form a stable form after the decay and are no longer radioactive, some elements have no stable form and are always radioactive. Uranium is such an element which is always radioactive.