How do electrons flow in AC? Electrons flow from low potential to high potential in DC, i.e. from negative terminal to positive terminal.
But how do they flow in AC, as the polarity changes every 10ms for 50Hz?
 A: It is worth copying this analysis of what a current is:

So the electrons only move with a drift velocity

Although your light turns on very quickly when you flip the switch, and you find it impossible to flip off the light and get in bed before the room goes dark, the actual drift velocity of electrons through copper wires is very slow. It is the change or "signal" which propagates along wires at essentially the speed of light.

italics mine.
Using the calculator given  for a copper wire of 1 mm the drift velocity is 0.94X10^-3m/s. 
The only difference between AC and DC is the forced change of direction with the AC frequency.
A: Electrons do not "flow" in AC unlike in DC, where they physically move from negative to the positive terminal of the EMF source. Observe that by definition current is rate of flow of charge. In alternating current, the electrons just oscillate about their mean position. Yet they constitute a current[alternating current here], because there is flow of charge through the cross section of the wire.
A: *

*If you plug a battery to a circuit, you have direct current (DC). Charge starts moving and speeding up from positive towards negative terminal. At some point they reach maximum speed and we have a constant steady current.

*If you now unplugged the battery, turned it around and reinserted it very quickly, the moving charge would slow down, stop shortly and start moving backwards, then speed up backwards and soon reach a steady flow.
If you could turn around the battery very, very fast, you would constantly see charges speeding up, slowing down, moving backwards, slowing down, moving forwards etc. Maybe so fast that the current never has time to becomes steady in any direction. You will then call it alternating current (AC).
A: The flow of electrons is overrated: even in DC they move at a rather leisurely pace (we are talking about fractions of inches per second in the mean).  What moves at near the speed of light is their mean displacement.
This displacement is a back-and-forth in AC.  Imagine sucking a bit of air at a straw in a glass of water and then blowing into it.  Most of the water in the straw will remain there, the speed with which you suck and blow can be quite relaxed, yet the level in the glass will fall and rise almost instantly.
