**Explanation:**

The correct way of designating fit is option 'C' which is "50 H8/g7".

**Explanation in detail:**

**1. Fit designations:**
In engineering, fit designations are used to specify the clearance or interference between two mating parts. The fit designation consists of two letters and a number. The first letter represents the lower deviation of the hole (internal feature) and the second letter represents the upper deviation of the shaft (external feature). The number represents the tolerance grade.

**2. H8/g7:**
In option 'C', the fit designation is "H8/g7". Let's break it down to understand the meaning of each component.

- **H8:** H8 represents the lower deviation of the hole (internal feature). The letter 'H' indicates a hole and the number '8' represents the tolerance grade. The tolerance grade determines the range of acceptable sizes for the hole. In this case, the hole size will have a lower deviation of H8.

- **g7:** g7 represents the upper deviation of the shaft (external feature). The letter 'g' indicates a shaft and the number '7' represents the tolerance grade. The tolerance grade determines the range of acceptable sizes for the shaft. In this case, the shaft size will have an upper deviation of g7.

**3. 50:**
The number '50' in option 'C' represents the fundamental deviation. The fundamental deviation is the algebraic difference between the basic size and the actual size of the feature. It is used to determine the fit type (clearance, transition, or interference). In this case, the fundamental deviation is 50.

**4. Conclusion:**
Therefore, the correct way of designating fit is "50 H8/g7" which indicates that the hole size will have a lower deviation of H8, the shaft size will have an upper deviation of g7, and the fundamental deviation is 50.