Which one of the following is a null set?

Question

Question

Answer 1

Concept:

The null set, also called the empty set, is the set that does not contain anything. It is symbolised as { }

Calculation:

1.Set contain value 0, so it is not a null set

2. We know, { } = ϕ, as it contains some value it is not a null set

3. This set contains ϕ , so this is also not a null set.

4. Here, x2 + 1 = 0

⇒ x² = -1

⇒ x = √-1 (whiich is not real)

But x ϵ R, so this set is a null set

Hence, option (4) is correct.