**Core Concept**
The movement of proteins from the nucleus to the cytoplasm is a critical process in cellular biology, involving the breakdown of nuclear proteins and their subsequent export. This process can be studied using various microscopic techniques that allow for the visualization of protein dynamics in live cells.

**Why the Correct Answer is Right**
FRAP (Fluorescence Recovery After Photobleaching) is a technique used to study protein dynamics in live cells. It involves photobleaching a small region of the cell, which causes the fluorescence of the protein of interest to decrease. The protein then diffuses back into the bleached region, and the rate of recovery can be measured to determine the mobility of the protein. In the context of nuclear-cytoplasmic transport, FRAP can be used to study the movement of proteins from the nucleus to the cytoplasm by photobleaching a nuclear region and measuring the recovery of fluorescence in the cytoplasm.

**Why Each Wrong Option is Incorrect**
**Option A:** FISH (Fluorescence In Situ Hybridization) is a technique used to visualize specific DNA or RNA sequences within cells, but it is not suitable for studying protein movement between the nucleus and cytoplasm.

**Option C:** Confocal microscopy is a high-resolution imaging technique that can be used to study the localization of proteins within cells, but it does not provide information on protein dynamics or movement.

**Option D:** Electron microscopy is a technique used to study the ultrastructure of cells, but it is not suitable for studying protein movement between the nucleus and cytoplasm due to its low resolution and inability to visualize live cells.

**Clinical Pearl / High-Yield Fact**
FRAP is a powerful technique for studying protein dynamics in live cells, but it requires careful consideration of the photobleaching time and intensity to avoid causing damage to the cell.

**Correct Answer:**
✓ Correct Answer: B. FRAP