In the given question option a) ( i.e the electric field is increasing ) is correct.
The above option is correct because the electric field and the electromagnetic wave both are in the same phase of the EM wave. Thus, the electromagnetic wave and the electric field are directly proportional to each other.
We don't know that at all. The 3rd law says that the REaction is opposite and EQUAL to the action. We don't know where that "twice as much" comes from.