Correct Option: B

We know that

x(t) = sgn (t) ↔	2
	jω

By using duality property if
x(t) → x(jω)
then x(t) → 2π x(– jω)

	2	= – 2π sgn (ω)
	jt

	2	= – 2π sgn (f)
	jt

or sgn (f) = –	1	×	j	=	j
	πjt		j		πt

Hence, alternative (B) is the correct choice.