Question

A trivalent impurity has ………………. valence electrons.
$
  (a){\text{ 4}} \\
  (b){\text{ 5}} \\
  (c){\text{ 6}} \\
  (d){\text{ 3}} \\
$

Answer 1

Hint: In this question use the concept that trivalent means three moreover the elements of group 13 are trivalent and are mixed with semiconductors as they act as impurities. This will help get the right number of valence electrons.

Complete Step-by-Step solution:
As the name suggests trivalent so it has three valence electrons.
For example ${13^{th}}$ group of elements are known as trivalent impurities which are mixed in pure semiconductor so that the conduction is possible.
The ${13^{th}}$ group of elements are B, Al, Ga, In and Tl.
Where B = boron, Al = aluminum, Ga = gallium, In = indium and Tl = thallium.
All have 3 valence electrons in its outer shell respectively.
So this is the required answer.
Hence option (D) is the correct answer.

Note – One very interesting fact about group 13 elements is that they have $n{s^2}n{p^1}$ valence electron configurations, and all tend to lose their three valence electrons to form compounds in the +3 oxidation state. For semiconductors doping of group 14 elements with group 13 elements produces holes in the crystal, thus p type semiconductors are produced.