Why pin 1 of IC7402 is output pin?

Pin 1 of the IC7402 is an output pin because it is part of a quad 2-input NOR gate configuration. Each NOR gate within the IC has specific input and output pins, and pin 1 corresponds to the output of the first NOR gate. The output pin provides the logical result of the NOR operation performed on the two input signals connected to the associated input pins.