parallel means they will never cross each other. take a example
when a resistance connected in parallel then a current flowing through it(both resistance) is not same depended on the value of each resistance. while in the series circuit current values is same for both resistance.
parallel lines are drawn below:-
series lines:-
-------
The NEVER cross each other
1 pair of parallel line
2
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none.
None
5
Just one. And the other pair cannot be parallel.
Two pairs.
None
2 pairs
2 pairs