Apache Spark - Which statement about the function passed to reduce in case...

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Which statement about the function passed to reduce in case of spark is not true?

It can only take two arguments
Both Arguments as well as the return value should be of same data type
This function will be executed sequentially not parallely over the RDD
If there are N elements in RDD, this function will be executed N-1 times.
This function must be commutative - order of arguments should not matter
This function must be associative - which two element are passed first shouldn't matter