Venturimeter is a device used to measure the flow rate of fluid in a pipe. It consists of four main parts arranged in a specific sequence. Let's understand the correct sequence of these parts:

1. Diverging Part:
The diverging part is the first component of the venturimeter. It is designed to gradually expand the flow area of the pipe. This allows the fluid to decelerate and convert its kinetic energy into potential energy. The diverging part helps in reducing the fluid's velocity and increasing the pressure.

2. Throat:
The throat is the narrowest part of the venturimeter. It is located immediately after the diverging part. The purpose of the throat is to accelerate the fluid flow by constricting the flow area. As the fluid passes through the throat, its velocity increases, and the pressure decreases due to the principle of continuity.

3. Main Inlet Pipe:
The main inlet pipe is the section of the venturimeter that leads the fluid into the diverging part. It is connected to the upstream section of the pipe from where the fluid is being measured. The main inlet pipe is responsible for directing the fluid flow towards the venturimeter and ensuring a smooth entry into the device.

4. Short Converging Part:
The short converging part is the final component of the venturimeter. It follows the throat and helps in gradually increasing the flow area of the pipe. This allows the fluid to decelerate further and recover its pressure energy. The short converging part assists in the transition of the fluid from the throat back to the original pipe diameter.

The correct sequence of the parts in a venturimeter is:
c) 3 4 2 1

Explanation:
The main inlet pipe (3) is connected to the upstream section of the pipe, directing the fluid towards the venturimeter. The short converging part (4) follows the throat and gradually increases the flow area. The throat (2) is the narrowest part where the fluid's velocity increases and pressure decreases. Finally, the diverging part (1) helps in reducing the fluid velocity and increasing the pressure.

Hence, the correct sequence of parts in a venturimeter is 3 4 2 1.