How many subsets does the set $\{a, b\}$ have?
A$2$
B$3$
C$4$
D$5$
Answer & Solution
Correct answer: C. $4$
A set with $n$ elements has $2^{n}$ subsets. For $n = 2$: $2^{2} = 4$.
List: $\phi$, $\{a\}$, $\{b\}$, $\{a, b\}$ — four subsets.
Trap **B**: forgets to count $\phi$ or the set itself.
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