**Core Concept**
Tall 'T' waves on an electrocardiogram (ECG) are indicative of hyperkalemia, a condition characterized by elevated potassium levels in the blood. This is due to the effect of potassium on the cardiac membrane potential, leading to changes in the repolarization phase of the cardiac action potential.

**Why the Correct Answer is Right**
In hyperkalemia, increased potassium ions (K+) affect the cardiac membrane potential, causing a shift in the resting membrane potential. This results in a more rapid depolarization of the cardiac cells, leading to an increase in the amplitude of the T wave on the ECG. The tall 'T' wave is a classic ECG finding in hyperkalemia, often preceding more severe cardiac conduction disturbances.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the ECG finding of tall 'T' waves. Other ECG changes associated with this option are not mentioned.
* **Option B:** While this option may be related to cardiac rhythm disturbances, it is not directly related to the specific ECG finding of tall 'T' waves.
* **Option C:** This option is incorrect as it does not directly relate to the ECG finding of tall 'T' waves. Other ECG changes associated with this option are not mentioned.

**Clinical Pearl / High-Yield Fact**
The ECG changes associated with hyperkalemia can be remembered using the mnemonic **"PEAKS"**, which stands for **P**rolonged QT interval, **E**levated T waves, **A**bsent P waves, **K**alectasis (peaked T waves), and **S**inusoidal rhythm. Early recognition of these changes is crucial for prompt management of hyperkalemia.

**Correct Answer: C. Hypokalemia**