18. NCERT Exemplar IX

 

  

Liquid A is a good conductor of electricity, allowing the maximum current to pass through it, which is sufficient to glow the bulb. But, when it is replaced by another liquid B, the bulb may not glow because the current through liquid A may be too weakcurrent through liquid B may be too weakconcentration of liquid B may be too weakions of quid B may be too low to glow the bulb. However, the lower ions of liquid B is enoughsmall current travelling through A is enoughsmall current travelling through B is enoughlow concentration of liquid B is enough to glow a low-voltage LED, so it glows.