Explanation

(c) An $n$-type semiconductor is formed by doping pure germanium or silicon crystal with suitable impurity atoms of valence five. As the impurity atoms take the positions of Ge atoms in germanium crystal, its four electrons form covalent bonds by sharing electrons with the neighbouring four atoms of germanium whereas the fifth electron is left free. Since, the atom on the whole is electricall neutral, the $n$-type semiconductor is also neutral.