The plasma is obtained by the ionization of a gas by means of an electrical discharge at high frequencies up to _______ 10 MHz 20 MHz 30 MHz None of these

To answer the question, we'll evaluate the given options regarding the frequency range of electrical discharges used for ionizing gas to obtain plasma.

Analysis of Frequency Ranges

1. 10 MHz: Represents a frequency suitable for certain plasma generation techniques.
2. 20 MHz: This frequency is also common in applications involving plasma.
3. 30 MHz: Higher frequency that can contribute to ionization processes.
4. None of these: Implies that none of the stated frequencies are applicable, indicating potentially higher or different technology frequencies.

Conclusion

Plasma generation typically uses radio frequencies ranging from a few kHz up to several MHz, and in many applications, frequencies around 13.56 MHz are commonly used. Given the options presented and looking for the highest frequency where plasma can still be efficiently generated, 20 MHz is a commonly recognized frequency.

Final Answer

20 MHz