Randomising Values in Dictionaries and displaying them in labels SWIFT

so i'm trying so that when I click a button, it displays a random key from my dictionary which i have and then i click another button and it displays the data associated with that key for a small memory science app I am making. For example, I click the button and in the label says Hydrogen, then I click another button and it gives my the data saying the formula "H". So how do I make the label give me a random key from the dictionary when I click the button?

Thanks, Riley

I'm in Xcode 9.4.1