1 occurs once
5 occurs once
6 occurs once
9 occurs twice
13 occurs twice
19 occurs once
34 occurs once
45 occurs once
We know that the mode of a set of observations is the observation that occurs most often.
Since 9 and 13 both occur twice, they both have the possibility of being modes.
But, the mode of the dataset is given to be 13, which means that 13 has to occur more number of times than 9.
So, the missing number is 13.