The correct answer is frequency.
In an ordinary transformer, the frequency of the alternating current (AC) input voltage is the same as the frequency of the AC output voltage. This is because the transformer works by electromagnetic induction, which is a process that does not change the frequency of an AC signal.
The voltage and current in a transformer can change, depending on the turns ratio of the transformer. The turns ratio is the number of turns in the primary winding divided by the number of turns in the secondary winding. The voltage ratio is equal to the turns ratio, and the current ratio is the inverse of the turns ratio.
For example, if a transformer has a turns ratio of 1:1, then the voltage and current in the primary and secondary windings will be the same. If the transformer has a turns ratio of 2:1, then the voltage in the secondary winding will be twice the voltage in the primary winding, and the current in the secondary winding will be half the current in the primary winding.
In conclusion, the frequency of an AC signal does not change in an ordinary transformer. The voltage and current can change, depending on the turns ratio of the transformer.