In the discharge tube emission the cathode rays requires:

Explanation

In a discharge tube, cathode rays are produced when electrons are emitted from the cathode and accelerated towards the anode. For this to occur efficiently, a high potential difference is necessary to provide the electrons with sufficient energy. Additionally, low pressure is critical because it reduces the number of gas molecules in the tube, allowing the electrons to travel freely without colliding with gas particles. **Option A** (Low potential and low pressure) is incorrect because insufficient potential fails to accelerate the electrons adequately, and low pressure can hinder the process of ionization. **Option B** (Low potential and high pressure) is also incorrect as high pressure would impede the movement of electrons, and low potential does not provide the necessary energy for cathode ray production. **Option C** (High potential and high pressure) is wrong because, although high potential is favorable, high pressure creates a barrier to electron travel, thus preventing effective cathode ray emission. Therefore, **Option D** (High potential and low pressure) is the only configuration that allows for effective cathode ray emission.