Forward Bias in Devices:

Forward bias is a condition in which the positive terminal of a voltage source is connected to the p-region of a diode, and the negative terminal is connected to the n-region. This forward biasing allows current to flow through the diode, enabling it to operate in its normal mode.

Solar Cell:
A solar cell is a device that converts sunlight directly into electricity. When sunlight strikes the solar cell, it generates electron-hole pairs, creating a voltage across the p-n junction. The solar cell is typically connected in a forward bias configuration, allowing the generated current to flow through an external circuit.

Laser Diode:
A laser diode is a semiconductor device that emits coherent light through stimulated emission. To operate, a laser diode is typically forward biased. The forward bias voltage provides the necessary energy for the stimulated emission process to occur, resulting in the emission of laser light.

Zener Diode:
A Zener diode is a special type of diode that operates in the reverse breakdown region. It is primarily used for voltage regulation. While a Zener diode can be operated in a forward bias mode, its normal mode of operation is in reverse bias, where it exhibits a controlled breakdown voltage.

Avalanche Photodiode:
An avalanche photodiode is a highly sensitive semiconductor device used to detect light. It operates in the reverse bias mode, where the reverse voltage applied across the diode creates an internal electric field. When photons strike the diode, they generate electron-hole pairs, which are then multiplied through an avalanche process. This multiplication is achieved by the high electric field, allowing for high sensitivity in detecting light.

Conclusion:
Based on the given options, the devices that are forward biased in their normal mode of operation are the solar cell and laser diode. The solar cell operates in a forward bias mode to convert sunlight into electricity, while the laser diode requires forward biasing to emit laser light. On the other hand, the Zener diode operates in reverse bias for voltage regulation, and the avalanche photodiode operates in reverse bias for light detection.