Question 4
What type of reaction is 2Na + 2H2O → 2NaOH + H2, and why?
The right answer is the one marked above.
A single displacement, because Na and H2 are lone elements. The sodium has displaced the hydrogen in the water and taken its place.
Two substances on each side make it tempting to call this a double displacement. The deciding sign is not the count but whether a lone element is present.