Which of the following is the **empty set** $\phi$?
A$\{0\}$
B$\{x : x \text{ is a natural number and } 1 < x < 2\}$
C$\{\phi\}$
D$\{x : x \text{ is a real number and } x^2 = 4\}$
Answer & Solution
Correct answer: B. $\{x : x \text{ is a natural number and } 1 < x < 2\}$
*No natural number lies strictly between 1 and 2* — so set **B** is empty.
- **A** $\{0\}$ contains the element $0$ — not empty.
- **C** $\{\phi\}$ contains one element (the empty set itself) — not empty.
- **D** $\{2, -2\}$ has two elements.
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