"I" symbol means the current goes through the system (imagine the 'I' being a line, like a circuit connecting [power to the device]) "O" symbol means the current does not go through the system. ( the circle is an open circuit, having no power flowing through it
Nitrogen molecule is diatomic, whereas other elements form tetraatomic molecules.
Answer:
your answer may be found on a website called "Thought.co"
once you get there just search "Examples of Chemical Reactions in Everyday Life" and it will give you some ideas :)