Phase shifts through an Op-Amp caused by the internal RC circuit:
The correct answer is option 'B', the internal RC circuit. In order to understand why this is the correct answer, let's first discuss what an Op-Amp is and how it works.

Op-Amp Basics:
An operational amplifier, or Op-Amp, is an electronic device that amplifies the difference between two input voltages. It has a high gain and is widely used in various electronic circuits. The Op-Amp consists of several internal components, including transistors, resistors, and capacitors, which work together to provide the desired amplification.

Internal RC Circuit:
The Op-Amp contains an internal RC circuit, which consists of a resistor (R) and a capacitor (C) connected in series or parallel. This RC circuit is responsible for the phase shift observed in the output signal.

Phase Shift:
Phase shift refers to the time delay or phase difference between the input and output signals of a circuit. In the case of an Op-Amp, the phase shift is caused by the internal RC circuit.

Explanation:
When an AC input signal is applied to an Op-Amp, it passes through the internal RC circuit. The capacitor in the RC circuit charges and discharges in response to the input signal, causing a time delay or phase shift in the output signal.

The amount of phase shift depends on the values of the resistor and capacitor in the internal RC circuit. The time constant (τ) of the RC circuit, given by the product of resistance and capacitance (τ = R * C), determines the extent of phase shift. A larger RC time constant results in a greater phase shift.

Importance of Negative Feedback:
While the internal RC circuit causes a phase shift, negative feedback is used to compensate for this phase shift and maintain the desired output. Negative feedback is achieved by connecting a feedback resistor (Rf) between the output and the inverting input of the Op-Amp.

The negative feedback helps to stabilize the Op-Amp's gain and reduces the effects of the internal RC circuit on the phase shift. By adjusting the value of the feedback resistor, the phase shift can be minimized, and the Op-Amp can function as an ideal amplifier with minimal distortion.

Conclusion:
In summary, phase shifts through an Op-Amp are primarily caused by the internal RC circuit. The capacitor in the RC circuit charges and discharges in response to the input signal, resulting in a time delay or phase shift in the output signal. However, negative feedback is used to compensate for this phase shift and maintain the desired output. By adjusting the value of the feedback resistor, the phase shift can be minimized, allowing the Op-Amp to operate as an ideal amplifier.