The cathode ray tube experiment: In this experiment which later give birth to the concept of electrons as constituent species of an atom, for testing the properties of the particles, (i)Thomson placed two oppositely-charged electric plates around the cathode ray. The cathode ray was deflected away from the negatively-charged electric plate (Cathode) and moved (particles) towards the positively-charged electrode (Anode)- Which was the clear indication of the cathode ray was composed of negatively-charged particles. (ii)Thomson also placed two magnets on either side of the cathode ray tube and observed that this magnetic field also deflected the cathode ray. Thomson repeated his experiments using different metals as electrode materials, and found that the properties of the cathode ray remained constant no matter what material originated the cathode.

The results of cathode ray discharge tube experiment, clearly shows that cathode rays consist of negatively charged particles i.e. electrons (discovered by William Crookes) and hence, the property of cathode rays (or electrons) neither depend on the material of electrodes ( therefore, option (iii) ) is correct) nor on the nature of the gas [present in cathode ray tube.

Other 2 options (i) They start from the cathode and move towards the anode and

(ii) They travel in a straight line in the absence of an external electrical or magnetic field (Fig. 4.(b)) are also correct as they are experimentally proved.