In a silicon intrinsic semiconductor, the forbidden energy gap between the valence band and the conduction band is approximately equal to

1.1 eV

The correct answer is Option (1) → 1.1 eV

In semiconductors, the forbidden energy gap $E_g$ is the energy difference between the valence band (highest energy band fully filled with electrons) and the conduction band (lowest empty band where electrons can move freely).

For intrinsic silicon at room temperature:

$E_g \approx 1.1 \, eV$

This means that about $1.1 \, eV$ of energy must be supplied (for example, by thermal excitation or photon absorption) to lift an electron from the valence band into the conduction band, allowing it to conduct electricity.