Introduction:
In the field of railway engineering, switches are an important component that allows trains to change tracks or shift from one line to another. A switch consists of a pair of tapered movable rails, known as tongue rail and heel rail, which are connected and fitted together with necessary connections and fittings. In this question, we are asked to identify the name of the rail that forms the switch.

Tongue Rail:
The correct answer to the question is option 'C', which is the tongue rail. The tongue rail is a tapered movable rail that forms the main part of the switch. It is designed in a way that it can be moved laterally to align with either the straight track or the diverging track. The tongue rail is located on the inside of the switch and is responsible for guiding the wheels of the train onto the desired track.

Heel Rail:
While the tongue rail is responsible for guiding the wheels onto the desired track, the heel rail provides support and stability to the train as it passes through the switch. The heel rail is located on the outside of the switch and is fixed in position. It is designed to ensure that the wheels of the train maintain proper alignment while passing through the switch.

Connections and Fittings:
In addition to the tongue rail and heel rail, a switch also consists of various connections and fittings that ensure the smooth operation of the switch. These include:

1. Stock Rail: The stock rail is a straight rail that is used to connect the switch to the main track. It provides a continuous path for the train to travel on.

2. Switch Point: The switch point is the point where the tongue rail and the stock rail meet. It is designed to allow the tongue rail to move laterally and align with either the straight track or the diverging track.

3. Switch Stand: The switch stand is a mechanical device that is used to control the movement of the switch. It allows the switch operator to manually move the tongue rail and align it with the desired track.

4. Switch Rod: The switch rod is a connecting rod that connects the switch stand to the tongue rail. When the switch stand is operated, it moves the switch rod, which in turn moves the tongue rail.

5. Guard Rail: The guard rail is an additional rail that is installed on the outside of the switch to prevent derailment. It provides an extra layer of protection and ensures that the wheels of the train stay on the track.

Conclusion:
In conclusion, a switch in railway engineering consists of a pair of tapered movable rails known as the tongue rail and heel rail. The tongue rail is responsible for guiding the wheels onto the desired track, while the heel rail provides stability and support. The switch also includes various connections and fittings such as the stock rail, switch point, switch stand, switch rod, and guard rail. These components work together to ensure the smooth and safe operation of the switch.