We are told that Alyssa needs 2 cups of flour for every 10 pancakes.
The ratio between cups and pancakes will be as follows:

Which, is we substitute our values we get:

As you can see, the ratio is a division between the two indicated values.
We can simplify the fraction of the answer if we divide both 2 and 10 by 2:

Answer:
the ratio is 1/5 (sometimes represented also as 1:5)