**Explanation:**

When selecting a voltmeter for measuring a high voltage of 50000 V direct current, the most suitable option would be an electrostatic voltmeter.

**Electrostatic voltmeter:**
An electrostatic voltmeter is a type of voltmeter that uses the principle of electrostatic forces to measure voltage. It consists of two fixed plates and one movable plate. When a voltage is applied across the fixed plates, an electrostatic force is generated, which causes the movable plate to move. The movement of the plate is proportional to the voltage being measured.

**Advantages of electrostatic voltmeter:**
- High accuracy: Electrostatic voltmeters are known for their high accuracy in voltage measurements.
- Wide measurement range: They can measure both low and high voltages, making them suitable for measuring 50000 V direct current.
- Insensitivity to current flow: Electrostatic voltmeters are not affected by the current flowing through the circuit, which makes them ideal for measuring high voltages without interference.

**Moving coil voltmeter:**
Moving coil voltmeters are commonly used for measuring low voltages. They operate on the principle of electromagnetic induction, where a coil moves in a magnetic field generated by a permanent magnet or electromagnet. However, they are not suitable for measuring high voltages like 50000 V as they are designed for lower voltage ranges.

**Hot wire voltmeter:**
Hot wire voltmeters measure voltage based on the heating effect of current passing through a wire. These voltmeters are typically used for measuring low to medium voltage ranges and are not suitable for measuring high voltages like 50000 V.

**Electrodynamometer:**
Electrodynamometer voltmeters are based on the interaction of magnetic fields produced by current-carrying coils. They are commonly used for measuring both AC and DC voltages. However, for a high voltage of 50000 V, an electrostatic voltmeter would be a better choice due to its higher accuracy and wider measurement range.

In conclusion, the most suitable voltmeter for measuring 50000 V direct current would be an electrostatic voltmeter.