What cannot be measured using a CRO device? 

The correct option is resistance. While a CRO cannot directly measure current, it can be done indirectly. Current can be interpreted from voltage readings if the resistance in the circuit is known (via Ohm's Law, V=IR), but the CRO itself doesn't directly measure current.

Additional Information 

• CRO is a very versatile instrument in the laboratory for measurement of voltage, current, frequency and phase angle of any electrical quantity.
• We cannot directly measure power by using CRO.
• The current is measured indirectly by measuring voltag drop across an impedance.
• A Lissajous figure is a pattern that is displayed on the screen when sinusoidal signals are applied to both horizontal & vertical deflection plates of CRO.
• These are used to measure the frequency of the given signals and  the phase difference between the signals.
• From the shape of the Lissajous pattern displayed on the CRO screen information about the relative phases of signals and the frequency ratio of signals can be determined.
• It is not used for precise measurement; it depends on the type of signals.
• If one frequency is an integral multiple (harmonic) of the other, the pattern will be steady. If not, the figure will not be stationary.