Question

Which pair of elements do not have stable configuration?
(A) Eu,Pm
(B) Gd, Lu
(C) Pd, Cd
(D) Am, Cm

Answer 1

Hint : To answer this question, we first need to understand what are elements. An element is a pure substance made up entirely of atoms with the same number of protons in their atomic nuclei, as defined by chemistry. Chemical elements, unlike chemical compounds, cannot be broken down chemically into simpler molecules.

Complete Step By Step Answer:
Electronic configuration - An element's electronic configuration is a symbolic representation of how its atoms' electrons are arranged across different atomic orbitals. When writing electron configurations, a standardized nomenclature is used, with the energy level and type of orbital stated first, then the number of electrons in the orbital put in superscript.
Stable configuration - Stability can also be predicted using electron configurations. When all of an atom's orbitals are filled, it is the most stable (and thus unreactive). The arrangements with the highest energy levels are the most stable. The noble gases have these configurations.
Unstable configuration - Other elements' atoms have an insecure electrical arrangement. Their valence shell isn't finished. They tend to add or lose electrons, or share electrons, in order to achieve a stable configuration of the nearest inert gas.
After generating gamma radiation, a radioactive element does not become stable unless it has also emitted some elementary particle, such as an electron or an alpha particle, which changes the isotope's identity. Each element can have many isotopes. The number of protons identifies the element.
So, with this we conclude that radioactive elements have non stable configuration.
So, the final answer is option (4) i.e., Am, Cm.

Note :
A radionuclide is an unstable atom that possesses too much nuclear energy. This extra energy can be released as gamma radiation from the nucleus, transferred to one of its electrons and released as a conversion electron, or used to generate and emit a new particle from the nucleus.