In the left hand side, it shows the time taken for cobalt chloride paper to turn pink in how many minutes. If you look at the graph, you can immediately notice that the bar labeled 'lower surface' in plant X section has the shortest bar. The taller the bar is, the quicker it took for cobalf chloeide paper to turn pink in an increasingly shorter amount of time.
The lower surface in plant X took only one minute for cobalt chloride to turn pink, while others took longer. This is the answer.
