If the lightbulb A in the circuit shown in the image burned out, the path for the current to flow is disrupted because one of its terminals is connected direct to the source. So, there will be no current through the lightbulbs B, C, and D, and they will turn off. Similarly it will happen, if the lightbulb D burned out.
If the lightbulb B burned out the current will continue circulating through the lightbulbs A, C, and D, because lightbulb B is connected in parallel. Similarly it will happen, if the lightbulb C burned out.
Mercury is very harmful to the average human being. the mercury can easily be released from the lamp if the lamp is knocked over and broken. mercury is also harmful if inhaled. sodium on the other hand is not harmful in any way.
Answer:
second one is correct that is right
