Question

There are many elements in the periodic table which exhibit variable valency. This is a particular characteristic of:
A. Representative elements
B. Transition elements
C. Noble gases
D. on-metals

Answer 1

Variable valency is nothing but different valencies shown by a single atom. An atom can show variable valencies depending upon the type of reaction it is undergoing.

Complete step by step answer:
Valency is nothing but the combining capacity of an element. Trying to achieve noble gas configuration to achieve stability the outer most orbit of the element is accepting or donating electrons and this property is known as valency of the atom.
Depending upon the type of reaction bonds are formed by donating, accepting or sharing electrons among atoms and hence they show variable valencies. For example, iron combines with oxygen to form ferrous oxide and ferric oxide as well. In ferrous oxide iron exhibits valency of $+2$ and in ferric oxide it shows the valency of $+3$ and hence iron shows variable valency.
Depending upon the result of the reaction, the products formed have different properties like magnetic properties, acidity or basicity or neutral.
Variable valencies are shown by elements having more than one valency or they exhibit more than one valency.
Transition elements show variable valency since they have vacant d orbital. The $(n-1)$d and ns electrons have the same energy level and hence take part in chemical bonding with more than valencies and hence, showing variable valency.

So, the correct answer is Option B.

Note: A few non metals such as nitrogen and oxygen also shows variable valencies but this is a characteristic property of transition elements. Also, noble gases have a fully filled orbital so they can’t show variable valencies.