Salt: NaCl
Hydrogen gas: H2
        
             
        
        
        
Base on the question all about the human eye were an optic nerve of it needs an energy of 2.10x10^-17J that could trigger a series of impulses that eventually reach to the brain. So the possible photons of blue light needed for for this energy is 52 photons
        
             
        
        
        
Answer:
4)experiments with cathode ray tubes
Explanation:
when sufficiently high voltage is applied across the electrods, current starts flowing through a stream of particles moving in the tube the negative electrode (cathode) to the positive electrode (anode). These were called Cathode Rays or Cathode Ray Particles