As you have seen in the Reading  Music UNIT 2 video, a  2/4 time signature means that there may be two crotchet beats (or equivalent notes) in each bar, which is indicated by the upper number (2) and the bottom number (4) indicates what type of note is going to be the unit of time, in this case, a crotchet.  

So, in a 2/4 bar, it is possible to find: a minim/ two crotches/ a crotchet and two quavers/ four quavers and it is possible to replace any of them with their corresponding rest. 

Let's see if you have got it. Drag the images of the staves to the corrrect column.