When an observation that is much larger than the rest of the data is added to a data set, the value of the median will increase substantially?

No. To compute the median, you arrange the whole dataset in increasing order, and pick the element in the middle. So, you have observations so far, you write the dataset as

And the median is the element in the middle, i.e

Now, assume you add the last observation, . This is much larger than the rest of the dataset, so if we arrange the dataset in increasing order, it will be the last:

But the median is always the element in the middle, so it is again either or

if i put something wrong your not gonna like it so rather not say nothing.