Question: Q. 3. Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to $\left(E_{g}\right){\mathrm{C}^{\prime}}\left(E{g}\right){\mathrm{Si}}$ and $\left(E{g}\right)_{\mathrm{Ge}}$ Which of the following statements is true?
(a) $\left(E_{g}\right){\mathrm{Si}}<\left(E{g}\right){\mathrm{Ge}}<\left(E{g}\right)_{\mathrm{C}}$.
(b) $\left(E_{g}\right){\mathrm{C}}<\left(E{g}\right){\mathrm{Ge}}>\left(E{g}\right){\mathrm{Si}}$. (c) $\left(E{g}\right){\mathrm{C}}>\left(E{g}\right){\mathrm{Si}}>\left(E{g}\right)_{\mathrm{Ge}}$.
(d) $\left(E_{g}\right){\mathrm{C}}=\left(E{g}\right){\mathrm{Si}}=\left(E{g}\right)_{\mathrm{Ge}}$.
[NCERT Exemplar]
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Solution:
Ans. Correct option : (c)
Explanation: Above mentioned three given elements, the energy band gap of carbon is the maximum and that of germanium is the least. The energy band gaps of these elements are related as : $\left(E_{g}\right){\mathrm{C}}>\left(E{g}\right){\mathrm{Si}}>\left(E{g}\right)_{\mathrm{Ge}}$
