Which of the following is a singleton set ?

$(x:|x|=5, x \in N)$ $(x:|x|=6, x \in Z)$ $\left(x: x^2+2 x+1=0, x \in N\right)$ $\left(x: x^2=7, x \in N\right)$

$(x:|x|=5, x \in N)$

|x| = 5  ⇒ x = 5     (∵ x ∈ N) Given set is singleton. Hence (1) is the correct answer.