Exploration. There are only two possible subsets of $\{1\}$, namely, $\varnothing$ and $\{1\}.$
a) List all possible subsets of $\{1,2\} .$ How many are there?
b) List all possible subsets of $\{1,2,3\} .$ How many are there?
c) Guess how many subsets there are of $\{1,2,3,4\} .$ Verif your guess by listing all the possible subsets.
d) How many subsets are there for $\{1,2,3, \dots, n\} ?$