Which of the following indicates that a silicon NPN junction transistor is biased on?
Why The base-emitter junction of a bipolar transistor is just a PN diode, and a forward-biased silicon junction sits at roughly 0.6 to 0.7 volts once it conducts. So measuring about 0.65 V from base to emitter (base positive for an NPN) tells you the transistor is turned on and base current is flowing. Germanium devices would show about 0.3 V instead, and the drop changes only slightly with current because the diode curve is so steep.
Watch out The resistance choices are distractors built from the same numbers: a biased junction is a nonlinear device, and an ohmmeter reading of a fraction of an ohm would indicate a shorted junction, not normal operation. The 6 to 7 volt option would destroy a typical base-emitter junction, which reverse breaks down around 5 to 7 volts and is not run forward anywhere near that.
Silicon diode drop 0.7 V, and B-E is a diode: look for VOLTS, not ohms, about 0.6 to 0.7.