Question

Variable valency is generally shown by:
A.Gaseous elements
B.Non-metals
C.s-block elements
D.d-block elements

Answer 1

Hint: Electrons, which are negatively charged particles, found in the outermost shell of an electron known as valence electrons. If the outermost shell is open then it can participate in the formation of a chemical bond.

Step by step answer: Valence or valency is the property of an element that tells the capacity of another atom with which an atom combines. For example,
Valency of hydrogen ${H_2}$ is 1.
Valency of Methane $C{H_4}$ is $C$=4 and $H$ =1.
Certain elements reveal more than one valency in their compounds are known as variable valency. Because of the different electronic configuration, they show variable valency.
Examples:
Transition metals like: Copper, Tin, Iron, Mercury etc.
For Iron: 2 valencies- ferrous oxide \[F{e^{2 + }}\] and ferric oxide $F{e^{3 + }}$.
Nonmetals like: Nitrogen and Oxygen.
As a reaction result, product forms differ in their properties with different valency atoms.
d block elements show variable valency because energy subshells (group of orbitals) 3d and 4s are very close. As a result, there is a possibility of losing an electron from both subshell 3d and 4s. Thus, they show variable oxidation state.
d block is also known as transition elements.
Thus, the correct option is D. i.e., d-block elements.

Additional Information: Distance of electrons depends on the orbit number. Orbit number higher than the distance of electrons is also greater. Orbits which are close to the nucleus, their electrons are more tightly held than those in the outer orbits.


Note: Remember energy level of subshells (n-1) d and ns are nearly the same. Electrons present in them take part in chemical bonding thus they show variable valencies. Many elements show variable valency to achieve stable electronic configuration.