Hint: Forbidden gap or band gap is same, for pure silicon at room temperature the forbidden gap or band gap is 1.1, that means the gap between the valance band and conduction band is called forbidden gap. This band implies without energy in the forbidden gap.
Complete step-by-step solution: The forbidden gap for pure silicon at room temperature is$1.1ev$. At room temperature the silicon falls under the semiconductors. Forbidden band means, the difference in the lower level of the conduction band and the upper level of the valence band is called forbidden gap. Forbidden gap or band gap plays a major role in determining the electrical conductivity of the material. Two adjacent bands simply are not wide enough because it has fully covered the range of energy. Band gap means the minimum amount of energy required for an electron to take a break between its bound state. Valence band electrons are tightly bound to the nucleus in the forbidden gap. Producing materials with different electrons and optical properties are the important concepts for the forbidden gap. The band decreases the temperature because the crystal lattice expands and the interatomic bonds are weak, weaker bonds means they contain less energy.
Note: In the above explanation we have learnt that the forbidden gap for pure silicon is$1.1eV$. Hence the correct option is b. The forbidden gap occurs only when the lower level and upper level are different. The band gap can be found only in the insulators of semiconductors.